diff --git a/.github/workflows/test-all.yml b/.github/workflows/test-all.yml
index f1ee1caab331..fa1c87fd937f 100644
--- a/.github/workflows/test-all.yml
+++ b/.github/workflows/test-all.yml
@@ -41,8 +41,8 @@ jobs:
     if: github.repository == 'react/react-native'
     outputs:
       any_code_change: ${{ steps.filter_exclusions.outputs.any_code_change == 'true' || github.event_name != 'pull_request' }}
-      should_test_android: ${{ steps.filter_exclusions.outputs.should_test_android == 'true' || github.event_name != 'pull_request' }}
-      should_test_ios: ${{ steps.filter_exclusions.outputs.should_test_ios == 'true' || github.event_name != 'pull_request' }}
+      should_test_android: ${{ steps.filter_exclusions.outputs.should_test_android == 'true' || steps.filter_inclusions.outputs.react_shared == 'true' || github.event_name != 'pull_request' }}
+      should_test_ios: ${{ steps.filter_exclusions.outputs.should_test_ios == 'true' || steps.filter_inclusions.outputs.react_shared == 'true' || github.event_name != 'pull_request' }}
       debugger_shell: ${{ steps.filter_inclusions.outputs.debugger_shell }}
     steps:
       - name: Checkout
@@ -85,6 +85,9 @@ jobs:
         id: filter_inclusions
         with:
           filters: |
+            # Shared Kotlin and its build configuration affect both platforms.
+            react_shared:
+              - 'packages/react-native/ReactShared/**'
             debugger_shell:
               - 'packages/debugger-shell/**'
               - 'scripts/debugger-shell/**'
diff --git a/.github/workflows/test-kmp.yml b/.github/workflows/test-kmp.yml
new file mode 100644
index 000000000000..b29eb07c2dd5
--- /dev/null
+++ b/.github/workflows/test-kmp.yml
@@ -0,0 +1,404 @@
+name: Test Kotlin Multiplatform pilot
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - '.github/workflows/test-kmp.yml'
+      - '.github/actions/setup-gradle/**'
+      - '.github/actions/setup-xcode/**'
+      - '.github/actions/setup-node/**'
+      - '.github/actions/yarn-install/**'
+      - 'Gemfile'
+      - 'Gemfile.lock'
+      - 'build.gradle.kts'
+      - 'gradle.properties'
+      - 'gradle/wrapper/**'
+      - 'settings.gradle.kts'
+      - 'yarn.lock'
+      - 'packages/rn-tester/Podfile'
+      - 'packages/rn-tester/RCTTest/**'
+      - 'packages/rn-tester/RNTesterPods.xcodeproj/**'
+      - 'packages/rn-tester/RNTester/RNTester.xctestplan'
+      - 'packages/react-native/ReactShared/**'
+      - 'packages/react-native/ReactAndroid/build.gradle.kts'
+      - 'packages/react-native/ReactAndroid/gradle.properties'
+      - 'packages/react-native/gradle/libs.versions.toml'
+      - 'packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/ColorStop.kt'
+      - 'packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/style/ColorStopTest.kt'
+      - 'packages/react-native/React/Fabric/Utils/RCTGradientUtils.*'
+      - 'packages/react-native/React/Fabric/RCTConversions.h'
+      - 'packages/react-native/Libraries/NativeAnimation/RCTAnimationUtils.*'
+      - 'packages/react-native/ReactCommon/react/renderer/graphics/**'
+      - 'packages/react-native/ReactCommon/react/utils/FloatComparison.h'
+      - 'packages/react-native/ReactCommon/react/utils/ManagedObjectWrapper.*'
+      - 'packages/react-native/React/React-RCTFabric.podspec'
+      - 'packages/react-native/React-Core.podspec'
+      - 'packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/**'
+      - 'packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/**'
+      - 'packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/scroll/**'
+      - 'packages/react-native/React/Base/RCTMultipartStreamReader.*'
+      - 'packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt'
+      - 'packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt'
+      - 'packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m'
+      - 'packages/react-native/scripts/react_native_pods.rb'
+      - 'packages/react-native/scripts/cocoapods/kmp.rb'
+      - 'packages/react-native/Package.swift'
+      - 'packages/react-native/package.json'
+      - 'packages/react-native/settings.gradle.kts'
+  push:
+    branches:
+      - main
+      - '*-stable'
+    paths:
+      - '.github/workflows/test-kmp.yml'
+      - '.github/actions/setup-gradle/**'
+      - '.github/actions/setup-xcode/**'
+      - '.github/actions/setup-node/**'
+      - '.github/actions/yarn-install/**'
+      - 'Gemfile'
+      - 'Gemfile.lock'
+      - 'build.gradle.kts'
+      - 'gradle.properties'
+      - 'gradle/wrapper/**'
+      - 'settings.gradle.kts'
+      - 'yarn.lock'
+      - 'packages/rn-tester/Podfile'
+      - 'packages/rn-tester/RCTTest/**'
+      - 'packages/rn-tester/RNTesterPods.xcodeproj/**'
+      - 'packages/rn-tester/RNTester/RNTester.xctestplan'
+      - 'packages/react-native/ReactShared/**'
+      - 'packages/react-native/ReactAndroid/build.gradle.kts'
+      - 'packages/react-native/ReactAndroid/gradle.properties'
+      - 'packages/react-native/gradle/libs.versions.toml'
+      - 'packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/ColorStop.kt'
+      - 'packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/style/ColorStopTest.kt'
+      - 'packages/react-native/React/Fabric/Utils/RCTGradientUtils.*'
+      - 'packages/react-native/React/Fabric/RCTConversions.h'
+      - 'packages/react-native/Libraries/NativeAnimation/RCTAnimationUtils.*'
+      - 'packages/react-native/ReactCommon/react/renderer/graphics/**'
+      - 'packages/react-native/ReactCommon/react/utils/FloatComparison.h'
+      - 'packages/react-native/ReactCommon/react/utils/ManagedObjectWrapper.*'
+      - 'packages/react-native/React/React-RCTFabric.podspec'
+      - 'packages/react-native/React-Core.podspec'
+      - 'packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/**'
+      - 'packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/**'
+      - 'packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/scroll/**'
+      - 'packages/react-native/React/Base/RCTMultipartStreamReader.*'
+      - 'packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt'
+      - 'packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt'
+      - 'packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m'
+      - 'packages/react-native/scripts/react_native_pods.rb'
+      - 'packages/react-native/scripts/cocoapods/kmp.rb'
+      - 'packages/react-native/Package.swift'
+      - 'packages/react-native/package.json'
+      - 'packages/react-native/settings.gradle.kts'
+
+permissions:
+  contents: read
+
+concurrency:
+  group: kmp-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test-shared:
+    runs-on: macos-26
+    timeout-minutes: 45
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - name: Set up JDK 17
+        uses: actions/setup-java@v5
+        with:
+          java-version: '17'
+          distribution: 'zulu'
+      - name: Set up Xcode for Kotlin Native
+        uses: ./.github/actions/setup-xcode
+        with:
+          xcode-version: '26.4.1'
+      - name: Set up Gradle
+        uses: ./.github/actions/setup-gradle
+      - name: Set up Ruby and CocoaPods
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.2.0'
+          bundler-cache: true
+      - name: Check CocoaPods linking configurations
+        run: bundle exec ruby packages/react-native/ReactShared/scripts/test-cocoapods-linking.rb
+      - name: Cache Kotlin Native toolchain
+        uses: actions/cache@v5
+        with:
+          path: ~/.konan
+          key: kmp-native-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('packages/react-native/ReactShared/*.gradle.kts', 'packages/react-native/ReactShared/gradle.properties', 'packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.properties') }}
+      - name: Test shared code on JVM and iOS
+        id: shared
+        working-directory: packages/react-native/ReactShared
+        run: >-
+          ./gradlew
+          jvmTest iosSimulatorArm64Test
+          linkDebugFrameworkIosArm64 linkReleaseFrameworkIosArm64
+          linkDebugFrameworkIosSimulatorArm64 linkReleaseFrameworkIosSimulatorArm64
+          linkDebugFrameworkIosX64 linkReleaseFrameworkIosX64
+          --stacktrace --console=plain
+      - name: Compare the Apple adapter with native gradients
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: ./scripts/test-apple-gradient.sh
+      - name: Compare optimized Apple gradients
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        env:
+          RCT_KMP_BUILD_TYPE: Release
+        run: ./scripts/test-apple-gradient.sh
+      - name: Compare native and shared multipart adapters
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: |
+          ./scripts/test-apple-multipart.sh
+          python3 scripts/test-android-multipart.py --max-workers 2
+      - name: Compare native and shared scroll snap adapters
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: python3 scripts/test-apple-scroll-snap.py --output "$RUNNER_TEMP/apple-scroll-snap" --benchmark-repeats 0
+      - name: Test packaged XCFramework consumption
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: ./scripts/test-apple-distribution.sh
+      - name: Test independent Kotlin runtime coexistence
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: python3 scripts/test-kotlin-coexistence.py
+      - name: Measure native gradient costs
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: python3 scripts/benchmark-apple-gradient.py
+      - name: Measure clean and incremental shared builds
+        if: ${{ !cancelled() && steps.shared.outcome == 'success' }}
+        working-directory: packages/react-native/ReactShared
+        run: python3 scripts/benchmark-kmp-build.py
+      - name: Upload test reports
+        if: always()
+        uses: actions/upload-artifact@v6
+        with:
+          name: kotlin-multiplatform-test-results
+          path: |
+            packages/react-native/ReactShared/build/reports/tests
+            packages/react-native/ReactShared/build/test-results
+            ${{ runner.temp }}/apple-scroll-snap/**/*.json
+            ${{ runner.temp }}/apple-scroll-snap/**/*.log
+            packages/react-native/ReactShared/build/apple-multipart-test/**/*.log
+            packages/react-native/ReactShared/build/android-multipart-test/build/test-results
+            packages/react-native/ReactShared/build/apple-distribution/**/*.json
+            packages/react-native/ReactShared/build/apple-distribution/**/*.log
+            packages/react-native/ReactShared/build/apple-distribution/**/consumer.xcresult
+            packages/react-native/ReactShared/build/kotlin-coexistence/**/*.json
+            packages/react-native/ReactShared/build/kotlin-coexistence/**/*.log
+            packages/react-native/ReactShared/build/apple-gradient-benchmark/**/*.json
+            packages/react-native/ReactShared/build/apple-gradient-benchmark/**/*.log
+            packages/react-native/ReactShared/build/kmp-build-benchmark/**/*.json
+            packages/react-native/ReactShared/build/kmp-build-benchmark/**/*.log
+          if-no-files-found: warn
+
+  test-android-consumers:
+    name: Android Maven and npm source consumers
+    runs-on: 8-core-ubuntu
+    timeout-minutes: 90
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+      - name: Set up Node
+        uses: ./.github/actions/setup-node
+      - name: Install JavaScript dependencies
+        uses: ./.github/actions/yarn-install
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - name: Set up JDK 17
+        uses: actions/setup-java@v5
+        with:
+          java-version: '17'
+          distribution: 'zulu'
+      - name: Set up Gradle
+        uses: ./.github/actions/setup-gradle
+      - name: Install Android build SDK
+        id: android-sdk
+        run: |
+          python3 - <<'PY'
+          import os, pathlib, re, shutil, subprocess, tomllib
+          versions = tomllib.loads(pathlib.Path('packages/react-native/gradle/libs.versions.toml').read_text())['versions']
+          sdkmanager = shutil.which('sdkmanager') or str(pathlib.Path(os.environ['ANDROID_HOME']) / 'cmdline-tools/latest/bin/sdkmanager')
+          packages = subprocess.check_output([sdkmanager, '--list'], text=True)
+          base = 'platforms;android-' + versions['compileSdk']
+          # Recent SDKs use a minor version in their package ID (for example android-37.0).
+          platform = next((name for name in [base + '.0', base] if re.search(r'^\s*' + re.escape(name) + r'\s*\|', packages, re.M)), None)
+          if platform is None:
+              raise SystemExit('No Android SDK package matches compileSdk ' + versions['compileSdk'])
+          subprocess.run([sdkmanager, platform, 'build-tools;' + versions['buildTools']], check=True)
+          with open(os.environ['GITHUB_OUTPUT'], 'a') as output:
+              output.write('ndk=' + versions['ndkVersion'] + '\n')
+          PY
+      - name: Enable emulator hardware acceleration
+        run: |
+          echo 'KERNEL=="kvm", GROUP="kvm", MODE="0666", OPTIONS+="static_node=kvm"' | sudo tee /etc/udev/rules.d/99-kvm4all.rules
+          sudo udevadm control --reload-rules
+          sudo udevadm trigger --name-match=kvm
+      - name: Build and run packaged Android consumers
+        uses: reactivecircus/android-emulator-runner@v2
+        with:
+          api-level: 35
+          target: google_apis
+          arch: x86_64
+          ndk: ${{ steps.android-sdk.outputs.ndk }}
+          cmake: 3.30.5
+          cores: 4
+          disable-animations: true
+          script: python3 packages/react-native/ReactShared/scripts/test-android-consumers.py --output-dir "$RUNNER_TEMP/kmp-android-consumers" --abi x86_64 --device emulator-5554
+      - name: Upload consumer reports
+        if: always()
+        uses: actions/upload-artifact@v6
+        with:
+          name: kmp-android-consumers
+          path: |
+            ${{ runner.temp }}/kmp-android-consumers/*.log
+            ${{ runner.temp }}/kmp-android-consumers/*.json
+          if-no-files-found: warn
+
+  test-apple-app:
+    name: RNTester KMP ${{ matrix.platform }} (${{ matrix.linkage }})
+    runs-on: macos-26
+    timeout-minutes: 90
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - platform: simulator
+            linkage: libraries
+          - platform: simulator
+            linkage: static
+          - platform: simulator
+            linkage: dynamic
+          - platform: device
+            linkage: libraries
+          - platform: catalyst
+            linkage: libraries
+    env:
+      RCT_KMP_APP_OUTPUT_DIR: ${{ github.workspace }}/packages/react-native/ReactShared/build/apple-app-results
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+      - name: Set up Node
+        uses: ./.github/actions/setup-node
+      - name: Install JavaScript dependencies
+        uses: ./.github/actions/yarn-install
+      - name: Select the Hermes compiler package
+        run: node scripts/releases/use-hermes-prebuilt.js
+      - name: Install the selected Hermes compiler
+        uses: ./.github/actions/yarn-install
+      - name: Set up JDK 17
+        uses: actions/setup-java@v5
+        with:
+          java-version: '17'
+          distribution: 'zulu'
+      - name: Set up Xcode for Kotlin Native
+        uses: ./.github/actions/setup-xcode
+        with:
+          xcode-version: '26.4.1'
+      - name: Set up Gradle
+        uses: ./.github/actions/setup-gradle
+      - name: Set up Ruby and CocoaPods
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.2.0'
+          bundler-cache: true
+      - name: Cache Kotlin Native toolchain
+        uses: actions/cache@v5
+        with:
+          path: ~/.konan
+          key: kmp-native-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('packages/react-native/ReactShared/*.gradle.kts', 'packages/react-native/ReactShared/gradle.properties', 'packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.properties') }}
+      - name: Build and validate the KMP source application
+        run: |
+          if [[ '${{ matrix.linkage }}' != libraries ]]; then
+            export USE_FRAMEWORKS='${{ matrix.linkage }}'
+          fi
+          ./packages/react-native/ReactShared/scripts/test-apple-app.sh '${{ matrix.platform }}'
+      - name: Upload application test reports
+        if: always()
+        uses: actions/upload-artifact@v6
+        with:
+          name: kmp-app-${{ matrix.platform }}-${{ matrix.linkage }}
+          path: |
+            ${{ env.RCT_KMP_APP_OUTPUT_DIR }}/*.log
+            ${{ env.RCT_KMP_APP_OUTPUT_DIR }}/*.json
+            ${{ env.RCT_KMP_APP_OUTPUT_DIR }}/*.txt
+            ${{ env.RCT_KMP_APP_OUTPUT_DIR }}/*.xcresult
+            ${{ env.RCT_KMP_APP_OUTPUT_DIR }}/Podfile*
+            ${{ env.RCT_KMP_APP_OUTPUT_DIR }}/project.pbxproj
+          if-no-files-found: warn
+
+  smoke:
+    runs-on: macos-26
+    timeout-minutes: 45
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+      - name: Set up JDK 17
+        uses: actions/setup-java@v5
+        with:
+          java-version: '17'
+          distribution: 'zulu'
+      - name: Set up Xcode
+        uses: ./.github/actions/setup-xcode
+        with:
+          xcode-version: '26.4.1'
+      - name: Set up Gradle
+        uses: ./.github/actions/setup-gradle
+      - name: Cache Kotlin Native toolchain
+        uses: actions/cache@v5
+        with:
+          path: ~/.konan
+          key: kmp-foundation-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('packages/react-native/ReactShared/*.gradle.kts', 'packages/react-native/ReactShared/gradle.properties', 'packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.properties') }}
+      - name: Test common code and build Apple frameworks
+        working-directory: packages/react-native/ReactShared
+        run: >-
+          ./gradlew -PreactNativeSharedSmoke=true
+          jvmTest iosSimulatorArm64Test
+          linkDebugFrameworkIosArm64 linkReleaseFrameworkIosArm64
+          linkDebugFrameworkIosSimulatorArm64 linkReleaseFrameworkIosSimulatorArm64
+          linkDebugFrameworkIosX64 linkReleaseFrameworkIosX64
+          --max-workers=2 --stacktrace --console=plain
+      - name: Test Objective-C consumption
+        working-directory: packages/react-native/ReactShared
+        run: ./scripts/test-apple-smoke.sh
+      - name: Verify nonempty tests and fixture isolation
+        working-directory: packages/react-native/ReactShared
+        run: |
+          ./gradlew jvmJar --max-workers=2 --console=plain
+          python3 - <<'PY'
+          from pathlib import Path
+          import xml.etree.ElementTree as ET
+          import zipfile
+          for target in ('jvmTest', 'iosSimulatorArm64Test'):
+              suites = [ET.parse(p).getroot() for p in Path('build/smoke/test-results', target).glob('TEST-*.xml')]
+              assert suites and sum(int(s.get('tests', 0)) for s in suites) > 0, target
+              assert all(not int(s.get(k, 0)) for s in suites for k in ('failures', 'errors', 'skipped')), target
+          jars = list(Path('build/libs').glob('*.jar'))
+          assert len(jars) == 1, jars
+          with zipfile.ZipFile(jars[0]) as jar:
+              assert not any('/smoke/' in name for name in jar.namelist()), 'Test fixture leaked into default output'
+          PY
+      - name: Upload smoke reports
+        if: always()
+        uses: actions/upload-artifact@v6
+        with:
+          name: kotlin-multiplatform-smoke-results
+          path: |
+            packages/react-native/ReactShared/build/smoke/reports/tests
+            packages/react-native/ReactShared/build/smoke/test-results
+            packages/react-native/ReactShared/build/smoke/apple-interop/*.log
+          if-no-files-found: warn
diff --git a/build.gradle.kts b/build.gradle.kts
index 19fcc1df1a66..c56aa5238203 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -72,6 +72,7 @@ nexusPublishing {
 tasks.register("clean", Delete::class.java) {
   description = "Remove all the build files and intermediate build outputs"
   dependsOn(gradle.includedBuild("gradle-plugin").task(":clean"))
+  dependsOn(gradle.includedBuild("react-native-shared").task(":clean"))
   subprojects.forEach {
     if (
         it.project.plugins.hasPlugin("com.android.library") ||
@@ -103,6 +104,7 @@ tasks.register("clean", Delete::class.java) {
 tasks.register("build") {
   description = "Build and test all the React Native relevant projects."
   dependsOn(gradle.includedBuild("gradle-plugin").task(":build"))
+  dependsOn(gradle.includedBuild("react-native-shared").task(":jvmTest"))
 }
 
 tasks.register("publishAllToMavenTempLocal") {
diff --git a/packages/react-native/Package.swift b/packages/react-native/Package.swift
index 386ca6958b7f..5e35ce276fdb 100644
--- a/packages/react-native/Package.swift
+++ b/packages/react-native/Package.swift
@@ -9,6 +9,10 @@
 import Foundation
 import PackageDescription
 
+if ProcessInfo.processInfo.environment["RCT_USE_KMP"] == "1" {
+  fatalError("RCT_USE_KMP=1 currently supports CocoaPods source builds only. Run RCT_USE_KMP=1 pod install in the iOS app; the SwiftPM prebuild does not include ReactNativeShared.")
+}
+
 let BUILD_FROM_SOURCE = false
 
 // Removing the legacy TurboModule and component interop layers is opt-in while those
diff --git a/packages/react-native/React-Core.podspec b/packages/react-native/React-Core.podspec
index 4e5802e7035d..1e209d256306 100644
--- a/packages/react-native/React-Core.podspec
+++ b/packages/react-native/React-Core.podspec
@@ -7,6 +7,10 @@ require "json"
 
 package = JSON.parse(File.read(File.join(__dir__, "package.json")))
 version = package['version']
+kmp_enabled = ENV['RCT_USE_KMP'] == '1'
+if kmp_enabled && ENV['RCT_USE_PREBUILT_RNCORE'] != '0'
+  raise 'RCT_USE_KMP=1 requires React Native core source builds. Use use_react_native! or set RCT_USE_PREBUILT_RNCORE=0.'
+end
 
 source = { :git => 'https://github.com/facebook/react-native.git' }
 if version == '1000.0.0'
@@ -54,13 +58,25 @@ Pod::Spec.new do |s|
   s.compiler_flags         = js_engine_flags()
   s.header_dir             = "React"
   s.weak_framework         = "JavaScriptCore"
-  s.pod_target_xcconfig    = {
+  pod_target_xcconfig     = {
                                "HEADER_SEARCH_PATHS" => header_search_paths,
                                "DEFINES_MODULE" => "YES",
                                "GCC_PREPROCESSOR_DEFINITIONS" => "RCT_METRO_PORT=${RCT_METRO_PORT}",
                                "CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard(),
                                "FRAMEWORK_SEARCH_PATHS" => frameworks_search_paths.join(" ")
                              }
+  if kmp_enabled
+    s.dependency 'React-KMP'
+    # React-Core is the common dependency of all Apple consumers. With dynamic
+    # pods it owns the Kotlin runtime once, even before Core calls a shared API.
+    # Static builds link the archive in the application via the post-install helper.
+    %w[iphoneos iphonesimulator].each do |sdk|
+      pod_target_xcconfig["GCC_PREPROCESSOR_DEFINITIONS[sdk=#{sdk}*]"] = '$(inherited) RCT_USE_KMP=1'
+      pod_target_xcconfig["FRAMEWORK_SEARCH_PATHS[sdk=#{sdk}*]"] = '$(inherited) "$(PODS_CONFIGURATION_BUILD_DIR)/ReactNativeSharedKMP"'
+      pod_target_xcconfig["OTHER_LDFLAGS[sdk=#{sdk}*]"] = '$(inherited) -ObjC -framework ReactNativeShared'
+    end
+  end
+  s.pod_target_xcconfig = pod_target_xcconfig
   s.user_target_xcconfig   = { "HEADER_SEARCH_PATHS" => "\"$(PODS_ROOT)/Headers/Private/React-Core\""}
   s.default_subspec        = "Default"
 
diff --git a/packages/react-native/React/Base/RCTMultipartStreamReader.m b/packages/react-native/React/Base/RCTMultipartStreamReader.m
index a57b9ea944bf..0ab5a7b23a77 100644
--- a/packages/react-native/React/Base/RCTMultipartStreamReader.m
+++ b/packages/react-native/React/Base/RCTMultipartStreamReader.m
@@ -7,6 +7,14 @@
 
 #import "RCTMultipartStreamReader.h"
 #import <QuartzCore/QuartzCore.h>
+#import <TargetConditionals.h>
+
+#if RCT_USE_KMP && TARGET_OS_IOS && !TARGET_OS_MACCATALYST
+#define RCT_MULTIPART_USE_KMP 1
+#import <ReactNativeShared/ReactNativeShared.h>
+#else
+#define RCT_MULTIPART_USE_KMP 0
+#endif
 
 #define CRLF @"\r\n"
 
@@ -30,6 +38,12 @@ - (NSDictionary *)parseHeaders:(NSData *)data
 {
   NSMutableDictionary *headers = [NSMutableDictionary new];
   NSString *text = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
+#if RCT_MULTIPART_USE_KMP
+  for (RNSMultipartHeader *header in [RNSMultipartHeaders.shared parseText:text ?: @""]) {
+    NSString *value = [header.value stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
+    [headers setValue:value forKey:header.name];
+  }
+#else
   NSArray<NSString *> *lines = [text componentsSeparatedByString:CRLF];
   for (NSString *line in lines) {
     NSUInteger location = [line rangeOfString:@":"].location;
@@ -41,6 +55,7 @@ - (NSDictionary *)parseHeaders:(NSData *)data
         stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
     [headers setValue:value forKey:key];
   }
+#endif
   return headers;
 }
 
@@ -84,13 +99,17 @@ - (void)emitProgress:(NSDictionary *)headers
 - (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
                           progressCallback:(RCTMultipartProgressCallback)progressCallback
 {
-  NSInteger chunkStart = 0;
-  NSInteger bytesSeen = 0;
-
   NSData *delimiter =
       [[NSString stringWithFormat:@"%@--%@%@", CRLF, _boundary, CRLF] dataUsingEncoding:NSUTF8StringEncoding];
   NSData *closeDelimiter =
       [[NSString stringWithFormat:@"%@--%@--%@", CRLF, _boundary, CRLF] dataUsingEncoding:NSUTF8StringEncoding];
+#if RCT_MULTIPART_USE_KMP
+  RNSMultipartFraming *framing = [[RNSMultipartFraming alloc] initWithDelimiterLength:(int32_t)delimiter.length
+                                                                 closeDelimiterLength:(int32_t)closeDelimiter.length];
+#else
+  NSInteger chunkStart = 0;
+  NSInteger bytesSeen = 0;
+#endif
   NSMutableData *content = [[NSMutableData alloc] initWithCapacity:1];
   NSDictionary *currentHeaders = nil;
   NSUInteger currentHeadersLength = 0;
@@ -101,9 +120,13 @@ - (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
   [_stream open];
   while (true) {
     BOOL isCloseDelimiter = NO;
-    // Search only a subset of chunk that we haven't seen before + few bytes
-    // to allow for the edge case when the delimiter is cut by read call
+#if RCT_MULTIPART_USE_KMP
+    NSInteger searchStart = [framing searchStartBufferOffset:0];
+    NSInteger chunkStart = [framing partStartBufferOffset:0];
+#else
+    // Preserve overlap when a delimiter is split between reads.
     NSInteger searchStart = MAX(bytesSeen - (NSInteger)closeDelimiter.length, chunkStart);
+#endif
     NSRange remainingBufferRange = NSMakeRange(searchStart, content.length - searchStart);
 
     // Check for delimiters.
@@ -113,6 +136,14 @@ - (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
       range = [content rangeOfData:closeDelimiter options:0 range:remainingBufferRange];
     }
 
+#if RCT_MULTIPART_USE_KMP
+    NSInteger index = range.location == NSNotFound ? -1 : (NSInteger)range.location;
+    RNSMultipartChunk *chunk = [framing nextChunkBufferLength:content.length
+                                                 bufferOffset:0
+                                               delimiterIndex:isCloseDelimiter ? -1 : index
+                                          closeDelimiterIndex:isCloseDelimiter ? index : -1];
+#endif
+
     if (range.location == NSNotFound) {
       if (currentHeaders == nil) {
         // Check for the headers delimiter.
@@ -131,7 +162,9 @@ - (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
                   callback:progressCallback];
       }
 
+#if !RCT_MULTIPART_USE_KMP
       bytesSeen = content.length;
+#endif
       NSInteger bytesRead = [_stream read:buffer maxLength:bufferLen];
       if (bytesRead <= 0 || _stream.streamError) {
         return NO;
@@ -140,12 +173,19 @@ - (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
       continue;
     }
 
+#if RCT_MULTIPART_USE_KMP
+    NSInteger chunkEnd = chunk.end;
+    BOOL isPart = chunk.isPart;
+    isCloseDelimiter = chunk.isLast;
+#else
     NSInteger chunkEnd = range.location;
-    NSInteger length = chunkEnd - chunkStart;
+    BOOL isPart = chunkStart > 0;
     bytesSeen = chunkEnd;
+#endif
+    NSInteger length = chunkEnd - chunkStart;
 
     // Ignore preamble
-    if (chunkStart > 0) {
+    if (isPart) {
       NSData *chunk = [content subdataWithRange:NSMakeRange(chunkStart, length)];
       [self emitProgress:currentHeaders
            contentLength:chunk.length - currentHeadersLength
@@ -160,7 +200,9 @@ - (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
       return YES;
     }
 
+#if !RCT_MULTIPART_USE_KMP
     chunkStart = chunkEnd + delimiter.length;
+#endif
   }
 }
 
diff --git a/packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTEnhancedScrollView.mm b/packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTEnhancedScrollView.mm
index b3481c1b98b4..3440d3799ca3 100644
--- a/packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTEnhancedScrollView.mm
+++ b/packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTEnhancedScrollView.mm
@@ -7,15 +7,44 @@
 
 #import "RCTEnhancedScrollView.h"
 #import <React/RCTUtils.h>
+#import <TargetConditionals.h>
 #import <react/utils/FloatComparison.h>
 
+#if RCT_USE_KMP && TARGET_OS_IOS && !TARGET_OS_MACCATALYST
+#define RCT_SCROLL_SNAP_USE_KMP 1
+#import <ReactNativeShared/ReactNativeShared.h>
+#else
+#define RCT_SCROLL_SNAP_USE_KMP 0
+#endif
+
 @interface RCTEnhancedScrollView () <UIScrollViewDelegate>
 @end
 
 @implementation RCTEnhancedScrollView {
   __weak id<UIScrollViewDelegate> _publicDelegate;
   BOOL _isSetContentOffsetDisabled;
+#if RCT_SCROLL_SNAP_USE_KMP
+  RNSScrollSnapOffsets *_sharedSnapOffsets;
+#endif
+}
+
+#if RCT_SCROLL_SNAP_USE_KMP
+@synthesize snapToOffsets = _snapToOffsets;
+
+- (void)setSnapToOffsets:(NSArray<NSNumber *> *)snapToOffsets
+{
+  _snapToOffsets = [snapToOffsets copy];
+  _sharedSnapOffsets = nil;
+  if (_snapToOffsets.count > 0) {
+    // Convert once per property update, retaining the existing floatValue precision.
+    RNSKotlinDoubleArray *offsets = [RNSKotlinDoubleArray arrayWithSize:(int32_t)_snapToOffsets.count];
+    for (NSUInteger i = 0; i < _snapToOffsets.count; i++) {
+      [offsets setIndex:(int32_t)i value:_snapToOffsets[i].floatValue];
+    }
+    _sharedSnapOffsets = [[RNSScrollSnapOffsets alloc] initWithOffsets:offsets];
+  }
 }
+#endif
 
 + (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key
 {
@@ -199,6 +228,15 @@ - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
 
     // Calculate the snap offsets adjacent to the initial offset target
     CGFloat targetOffset = isHorizontal ? targetContentOffset->x : targetContentOffset->y;
+#if RCT_SCROLL_SNAP_USE_KMP
+    targetOffset = [_sharedSnapOffsets resolveCurrentOffset:offsetAlongAxis
+                                               targetOffset:targetOffset
+                                              maximumOffset:maximumOffset
+                                                   velocity:velocityAlongAxis
+                                                snapToStart:self.snapToStart
+                                                  snapToEnd:self.snapToEnd]
+                       .targetOffset;
+#else
     CGFloat smallerOffset = 0.0;
     CGFloat largerOffset = maximumOffset;
 
@@ -250,6 +288,7 @@ - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
 
     // Make sure the new offset isn't out of bounds
     targetOffset = MIN(MAX(0, targetOffset), maximumOffset);
+#endif
 
     // Set new targetContentOffset
     if (isHorizontal) {
diff --git a/packages/react-native/React/Fabric/Utils/RCTGradientUtils.mm b/packages/react-native/React/Fabric/Utils/RCTGradientUtils.mm
index ee0f5ff8e0c9..8efb481a1d6f 100644
--- a/packages/react-native/React/Fabric/Utils/RCTGradientUtils.mm
+++ b/packages/react-native/React/Fabric/Utils/RCTGradientUtils.mm
@@ -8,10 +8,18 @@
 #import "RCTGradientUtils.h"
 #import <React/RCTAnimationUtils.h>
 #import <React/RCTConversions.h>
+#import <TargetConditionals.h>
 #import <react/utils/FloatComparison.h>
 #include <optional>
 #import <vector>
 
+#if RCT_USE_KMP && TARGET_OS_IOS && !TARGET_OS_MACCATALYST
+#define RCT_GRADIENT_USE_KMP 1
+#import <ReactNativeShared/ReactNativeShared.h>
+#else
+#define RCT_GRADIENT_USE_KMP 0
+#endif
+
 using namespace facebook::react;
 
 namespace {
@@ -156,6 +164,45 @@ CGSize calculateMultipliers(CGSize bounds)
   return std::nullopt;
 }
 
+#if RCT_GRADIENT_USE_KMP
+static std::vector<ProcessedColorStop> resolveSharedColorStops(
+    const std::vector<ColorStop> &colorStops,
+    CGFloat gradientLineLength)
+{
+  NSMutableArray<RNSGradientStopInput *> *inputs = [NSMutableArray arrayWithCapacity:colorStops.size()];
+  for (const auto &stop : colorStops) {
+    auto position = resolveColorStopPosition(stop.position, gradientLineLength);
+    RNSDouble *boxedPosition = position.has_value() ? [RNSDouble numberWithDouble:position.value()] : nil;
+    auto input = [[RNSGradientStopInput alloc] initWithPosition:boxedPosition hasColor:static_cast<bool>(stop.color)];
+    [inputs addObject:input];
+  }
+
+  auto resolved = [RNSGradientStops.shared resolveStops:inputs epsilon:kDefaultEpsilon useDoublePrecision:YES];
+  std::vector<ProcessedColorStop> result;
+  result.reserve(resolved.count);
+  NSArray<NSNumber *> *inputRange = @[ @0.0, @1.0 ];
+  for (RNSResolvedGradientStop *stop in resolved) {
+    const auto &leftColor = colorStops[stop.leftColorIndex].color;
+    SharedColor color;
+    if (stop.leftColorIndex == stop.rightColorIndex) {
+      // Preserve the original native color, including dynamic UIColor behavior.
+      color = leftColor;
+    } else if (std::isfinite(stop.weight)) {
+      const auto &rightColor = colorStops[stop.rightColorIndex].color;
+      NSArray<UIColor *> *outputRange =
+          @[ RCTUIColorFromSharedColor(leftColor), RCTUIColorFromSharedColor(rightColor) ];
+      auto interpolatedColor = RCTInterpolateColorInRange(stop.weight, inputRange, outputRange);
+      auto alpha = (interpolatedColor >> 24) & 0xFF;
+      auto red = (interpolatedColor >> 16) & 0xFF;
+      auto green = (interpolatedColor >> 8) & 0xFF;
+      auto blue = interpolatedColor & 0xFF;
+      color = colorFromRGBA(red, green, blue, alpha);
+    }
+    result.push_back({.color = color, .position = stop.position});
+  }
+  return result;
+}
+#else
 // Spec: https://drafts.csswg.org/css-images-4/#coloring-gradient-line (Refer transition hint section)
 // Browsers add 9 intermediate color stops when a transition hint is present
 // Algorithm is referred from Blink engine
@@ -261,12 +308,16 @@ CGSize calculateMultipliers(CGSize bounds)
 
   return colorStops;
 }
+#endif
 
 @implementation RCTGradientUtils
 // https://drafts.csswg.org/css-images-4/#color-stop-fixup
 + (std::vector<ProcessedColorStop>)getFixedColorStops:(const std::vector<ColorStop> &)colorStops
                                    gradientLineLength:(CGFloat)gradientLineLength
 {
+#if RCT_GRADIENT_USE_KMP
+  return resolveSharedColorStops(colorStops, gradientLineLength);
+#else
   if (colorStops.empty()) {
     return {};
   }
@@ -334,6 +385,7 @@ @implementation RCTGradientUtils
     }
   }
   return processColorTransitionHints(fixedColorStops);
+#endif
 }
 
 // CAGradientLayer linear gradient squishes the non-square gradient to square gradient.
diff --git a/packages/react-native/React/React-RCTFabric.podspec b/packages/react-native/React/React-RCTFabric.podspec
index 121669d1fa0e..92b4de666d5b 100644
--- a/packages/react-native/React/React-RCTFabric.podspec
+++ b/packages/react-native/React/React-RCTFabric.podspec
@@ -17,6 +17,10 @@ else
 end
 
 new_arch_flags = ENV['RCT_NEW_ARCH_ENABLED'] == '1' ? ' -DRCT_NEW_ARCH_ENABLED=1' : ''
+kmp_enabled = ENV['RCT_USE_KMP'] == '1'
+if kmp_enabled && ENV['RCT_USE_PREBUILT_RNCORE'] != '0'
+  raise 'RCT_USE_KMP=1 requires React Native core source builds. Use use_react_native! or set RCT_USE_PREBUILT_RNCORE=0.'
+end
 
 header_search_paths = [
   "\"$(PODS_TARGET_SRCROOT)/ReactCommon\"",
@@ -50,13 +54,24 @@ Pod::Spec.new do |s|
   s.module_name            = module_name
   s.weak_framework         = "JavaScriptCore"
   s.framework              = "MobileCoreServices"
-  s.pod_target_xcconfig    = {
+  pod_target_xcconfig = {
     "HEADER_SEARCH_PATHS" => header_search_paths,
     "OTHER_CFLAGS" => "$(inherited) " + new_arch_flags,
     "CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard()
   }.merge!(ENV['USE_FRAMEWORKS'] != nil ? {
     "PUBLIC_HEADERS_FOLDER_PATH" => "#{module_name}.framework/Headers/#{header_dir}"
   }: {})
+  if kmp_enabled
+    # Catalyst has no Kotlin/Native target. Its build keeps the existing implementation.
+    s.dependency 'React-KMP'
+    pod_target_xcconfig.merge!({
+      'GCC_PREPROCESSOR_DEFINITIONS[sdk=iphoneos*]' => '$(inherited) RCT_USE_KMP=1',
+      'GCC_PREPROCESSOR_DEFINITIONS[sdk=iphonesimulator*]' => '$(inherited) RCT_USE_KMP=1',
+      'FRAMEWORK_SEARCH_PATHS[sdk=iphoneos*]' => '$(inherited) "$(PODS_CONFIGURATION_BUILD_DIR)/ReactNativeSharedKMP"',
+      'FRAMEWORK_SEARCH_PATHS[sdk=iphonesimulator*]' => '$(inherited) "$(PODS_CONFIGURATION_BUILD_DIR)/ReactNativeSharedKMP"',
+    })
+  end
+  s.pod_target_xcconfig = pod_target_xcconfig
 
   s.dependency "React-Core"
   s.dependency "React-RCTImage"
diff --git a/packages/react-native/ReactAndroid/build.gradle.kts b/packages/react-native/ReactAndroid/build.gradle.kts
index f792d51a8567..f548f678cf58 100644
--- a/packages/react-native/ReactAndroid/build.gradle.kts
+++ b/packages/react-native/ReactAndroid/build.gradle.kts
@@ -717,6 +717,12 @@ tasks.withType<KotlinCompile>().configureEach {
 }
 
 dependencies {
+  // Embed the common Kotlin implementation in react-android's AAR. This keeps published
+  // consumers on the existing artifact instead of requiring a separate KMP publication.
+  implementation(
+      files("$reactNativeRootDir/ReactShared/build/android/react-native-shared.jar")
+          .builtBy(gradle.includedBuild("react-native-shared").task(":exportAndroidJar"))
+  )
   api(libs.androidx.appcompat)
   api(libs.androidx.appcompat.resources)
   api(libs.androidx.autofill)
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt
index f7d4d12d4b93..8e7eb1173ff8 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt
@@ -9,6 +9,8 @@
 
 package com.facebook.react.devsupport
 
+import com.facebook.react.shared.MultipartFraming
+import com.facebook.react.shared.MultipartHeaders
 import java.io.IOException
 import java.util.TreeMap
 import kotlin.math.max
@@ -52,30 +54,22 @@ internal class MultipartStreamReader(
     // throughput and fewer syscalls. For a 2MB bundle: ~128 reads instead of ~512.
     // Memory impact is negligible (12KB increase) while I/O overhead is significantly reduced.
     val bufferLen = 16 * 1024
-    var chunkStart: Long = 0
-    var bytesSeen: Long = 0
+    val framing = MultipartFraming(delimiter.size(), closeDelimiter.size())
+    var bufferOffset = 0L
     val content = Buffer()
 
     var currentHeaders: Map<String, String>? = null
     var currentBodyStartIndexInContent: Long = -1
 
     while (true) {
-      var isCloseDelimiter = false
-
-      // Search only a subset of chunk that we haven't seen before + few bytes
-      // to allow for the edge case when the delimiter is cut by read call.
-      val searchStart =
-          max((bytesSeen - closeDelimiter.size()).toDouble(), chunkStart.toDouble()).toLong()
-
-      var indexOfDelimiter = content.indexOf(delimiter, searchStart)
-      if (indexOfDelimiter == -1L) {
-        isCloseDelimiter = true
-        indexOfDelimiter = content.indexOf(closeDelimiter, searchStart)
-      }
-
-      if (indexOfDelimiter == -1L) {
-        bytesSeen = content.size()
-
+      val searchStart = framing.searchStart(bufferOffset)
+      val indexOfDelimiter = content.indexOf(delimiter, searchStart)
+      val indexOfCloseDelimiter =
+          if (indexOfDelimiter < 0) content.indexOf(closeDelimiter, searchStart) else -1L
+      val chunk =
+          framing.nextChunk(content.size(), bufferOffset, indexOfDelimiter, indexOfCloseDelimiter)
+
+      if (chunk == null) {
         if (currentHeaders == null) {
           val indexOfHeadersDelimiter = content.indexOf(headersDelimiter, searchStart)
           if (indexOfHeadersDelimiter >= 0) {
@@ -97,29 +91,27 @@ internal class MultipartStreamReader(
         continue
       }
 
-      val chunkEnd = indexOfDelimiter
-      val length = chunkEnd - chunkStart
+      val chunkEnd = chunk.end
+      val length = chunkEnd - chunk.start
 
       // Ignore preamble
-      if (chunkStart > 0) {
+      if (chunk.isPart) {
         if (currentHeaders != null && currentBodyStartIndexInContent >= 0) {
           val loadedFinal = max(0L, chunkEnd - currentBodyStartIndexInContent)
           emitProgress(currentHeaders, loadedFinal, true, listener)
         }
-        content.skip(chunkStart)
-        emitChunk(content, length, isCloseDelimiter, listener)
+        content.skip(chunk.start)
+        emitChunk(content, length, chunk.isLast, listener)
 
         currentHeaders = null
         currentBodyStartIndexInContent = -1
       } else {
         content.skip(chunkEnd)
       }
-      if (isCloseDelimiter) {
+      if (chunk.isLast) {
         return true
       }
-
-      chunkStart = delimiter.size().toLong()
-      bytesSeen = chunkStart
+      bufferOffset += chunkEnd
     }
   }
 
@@ -127,14 +119,9 @@ internal class MultipartStreamReader(
     // Header names are case-insensitive
     val headers: MutableMap<String, String> = TreeMap(String.CASE_INSENSITIVE_ORDER)
     val text = data.readUtf8()
-    val lines = text.split(CRLF.toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
-    for (line in lines) {
-      val indexOfSeparator = line.indexOf(":")
-      if (indexOfSeparator == -1) {
-        continue
-      }
-      val key = line.substring(0, indexOfSeparator).trim { it <= ' ' }
-      val value = line.substring(indexOfSeparator + 1).trim { it <= ' ' }
+    for (header in MultipartHeaders.parse(text)) {
+      val key = header.name.trim { it <= ' ' }
+      val value = header.value.trim { it <= ' ' }
       headers[key] = value
     }
     return headers
@@ -156,7 +143,7 @@ internal class MultipartStreamReader(
     val marker: ByteString = ByteString.encodeUtf8(CRLF + CRLF)
     val indexOfMarker = content.indexOf(marker, 0)
 
-    if (indexOfMarker == -1L || indexOfMarker >= chunkLength) {
+    if (indexOfMarker == -1L || indexOfMarker > chunkLength - marker.size()) {
       // No headers marker found inside the chunk. Treat the entire chunk as body.
       val bodyLength = chunkLength
       val body = Okio.buffer(FixedLengthSource(content, bodyLength))
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/ColorStop.kt b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/ColorStop.kt
index 32e101bcbcf1..c2a0eab93a38 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/ColorStop.kt
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/uimanager/style/ColorStop.kt
@@ -8,11 +8,11 @@
 package com.facebook.react.uimanager.style
 
 import androidx.core.graphics.ColorUtils
-import com.facebook.react.uimanager.FloatUtil
+import com.facebook.react.shared.GradientStopInput
+import com.facebook.react.shared.GradientStops
 import com.facebook.react.uimanager.LengthPercentage
 import com.facebook.react.uimanager.LengthPercentageType
 import com.facebook.react.uimanager.PixelUtil
-import kotlin.math.ln
 
 /**
  * Represents a color stop in a gradient as specified by the user.
@@ -68,170 +68,25 @@ internal object ColorStopUtils {
       colorStops: List<ColorStop>,
       gradientLineLength: Float,
   ): List<ProcessedColorStop> {
-    val fixedColorStops = Array<ProcessedColorStop>(colorStops.size) { ProcessedColorStop() }
-    var hasNullPositions = false
-    var maxPositionSoFar =
-        resolveColorStopPosition(colorStops[0].position, gradientLineLength) ?: 0f
-
-    for (i in colorStops.indices) {
-      val colorStop = colorStops[i]
-      var newPosition = resolveColorStopPosition(colorStop.position, gradientLineLength)
-
-      // Step 1:
-      // If the first color stop does not have a position,
-      // set its position to 0%. If the last color stop does not have a position,
-      // set its position to 100%.
-      newPosition =
-          newPosition
-              ?: when (i) {
-                0 -> 0f
-                colorStops.size - 1 -> 1f
-                else -> null
-              }
-
-      // Step 2:
-      // If a color stop or transition hint has a position
-      // that is less than the specified position of any color stop or transition hint
-      // before it in the list, set its position to be equal to the
-      // largest specified position of any color stop or transition hint before it.
-      if (newPosition != null) {
-        newPosition = maxOf(newPosition, maxPositionSoFar)
-        fixedColorStops[i] = ProcessedColorStop(colorStop.color, newPosition)
-        maxPositionSoFar = newPosition
-      } else {
-        hasNullPositions = true
-      }
-    }
-
-    // Step 3:
-    // If any color stop still does not have a position,
-    // then, for each run of adjacent color stops without positions,
-    // set their positions so that they are evenly spaced between the preceding and
-    // following color stops with positions.
-    if (hasNullPositions) {
-      var lastDefinedIndex = 0
-      for (i in 1 until fixedColorStops.size) {
-        val endPosition = fixedColorStops[i].position
-        val startPosition = fixedColorStops[lastDefinedIndex].position
-        val unpositionedStops = i - lastDefinedIndex - 1
-        if (endPosition != null && startPosition != null && unpositionedStops > 0) {
-          val increment = (endPosition - startPosition) / (unpositionedStops + 1)
-          for (j in 1..unpositionedStops) {
-            fixedColorStops[lastDefinedIndex + j] =
-                ProcessedColorStop(
-                    colorStops[lastDefinedIndex + j].color,
-                    startPosition + increment * j,
-                )
-          }
-          lastDefinedIndex = i
-        } else if (endPosition != null) {
-          // Current stop has a defined position but there are no unpositioned
-          // stops between lastDefinedIndex and i. Still need to advance
-          // lastDefinedIndex so that subsequent interpolation uses the
-          // correct start point instead of stale data.
-          lastDefinedIndex = i
+    val inputs =
+        colorStops.map { stop ->
+          GradientStopInput(
+              resolveColorStopPosition(stop.position, gradientLineLength)?.toDouble(),
+              stop.color != null,
+          )
         }
-      }
-    }
-
-    return processColorTransitionHints(fixedColorStops)
-  }
-
-  // Spec: https://drafts.csswg.org/css-images-4/#coloring-gradient-line (Refer transition hint
-  // section)
-  // Browsers add 9 intermediate color stops when a transition hint is present
-  // Algorithm is referred from Blink engine
-  // [source](https://github.com/chromium/chromium/blob/a296b1bad6dc1ed9d751b7528f7ca2134227b828/third_party/blink/renderer/core/css/css_gradient_value.cc#L240).
-  private fun processColorTransitionHints(
-      originalStops: Array<ProcessedColorStop>,
-  ): List<ProcessedColorStop> {
-    val colorStops = originalStops.toMutableList()
-    var indexOffset = 0
-
-    for (i in 1 until originalStops.size - 1) {
-      // Skip if not a color hint
-      if (originalStops[i].color != null) {
-        continue
-      }
-
-      val x = i + indexOffset
-      if (x < 1) {
-        continue
-      }
-
-      val offsetLeft = colorStops[x - 1].position
-      val offsetRight = colorStops[x + 1].position
-      val offset = colorStops[x].position
-      if (offsetLeft == null || offsetRight == null || offset == null) {
-        continue
-      }
-      val leftDist = offset - offsetLeft
-      val rightDist = offsetRight - offset
-      val totalDist = offsetRight - offsetLeft
-      val leftColor = colorStops[x - 1].color
-      val rightColor = colorStops[x + 1].color
-
-      if (FloatUtil.floatsEqual(leftDist, rightDist)) {
-        colorStops.removeAt(x)
-        --indexOffset
-        continue
-      }
-
-      if (FloatUtil.floatsEqual(leftDist, 0f)) {
-        colorStops[x].color = rightColor
-        continue
-      }
-
-      if (FloatUtil.floatsEqual(rightDist, 0f)) {
-        colorStops[x].color = leftColor
-        continue
-      }
-
-      val newStops = ArrayList<ProcessedColorStop>(9)
-
-      // Position the new color stops
-      if (leftDist > rightDist) {
-        for (y in 0..6) {
-          newStops.add(ProcessedColorStop(null, offsetLeft + leftDist * ((7f + y) / 13f)))
-        }
-        newStops.add(ProcessedColorStop(null, offset + rightDist * (1f / 3f)))
-        newStops.add(ProcessedColorStop(null, offset + rightDist * (2f / 3f)))
-      } else {
-        newStops.add(ProcessedColorStop(null, offsetLeft + leftDist * (1f / 3f)))
-        newStops.add(ProcessedColorStop(null, offsetLeft + leftDist * (2f / 3f)))
-        for (y in 0..6) {
-          newStops.add(ProcessedColorStop(null, offset + rightDist * (y / 13f)))
-        }
-      }
-
-      // Calculate colors for the new stops
-      val hintRelativeOffset = leftDist / totalDist
-      val logRatio = ln(0.5) / ln(hintRelativeOffset)
-
-      for (newStop in newStops) {
-        if (newStop.position == null) {
-          continue
-        }
-        val pointRelativeOffset = (newStop.position - offsetLeft) / totalDist
-        val weighting = Math.pow(pointRelativeOffset.toDouble(), logRatio).toFloat()
-
-        if (!weighting.isFinite() || weighting.isNaN()) {
-          continue
-        }
-
-        // Interpolate color using the calculated weighting
-        leftColor?.let { left ->
-          rightColor?.let { right -> newStop.color = ColorUtils.blendARGB(left, right, weighting) }
-        }
-      }
-
-      // Replace the color hint with new color stops
-      colorStops.removeAt(x)
-      colorStops.addAll(x, newStops)
-      indexOffset += 8
+    return GradientStops.resolve(inputs, epsilon = .00001f.toDouble()).map { stop ->
+      val leftColor = colorStops[stop.leftColorIndex].color
+      val rightColor = colorStops[stop.rightColorIndex].color
+      val weighting = stop.weight.toFloat()
+      val color =
+          when {
+            stop.leftColorIndex == stop.rightColorIndex -> leftColor
+            leftColor == null || rightColor == null || !weighting.isFinite() -> null
+            else -> ColorUtils.blendARGB(leftColor, rightColor, weighting)
+          }
+      ProcessedColorStop(color, stop.position.toFloat())
     }
-
-    return colorStops
   }
 
   private fun resolveColorStopPosition(
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.kt b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.kt
index 1bfb84f45368..1000cad9cf66 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.kt
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.kt
@@ -35,6 +35,8 @@ import com.facebook.react.R
 import com.facebook.react.common.ReactConstants
 import com.facebook.react.common.build.ReactBuildConfig
 import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags
+import com.facebook.react.shared.ScrollSnapDirection
+import com.facebook.react.shared.ScrollSnapOffsets
 import com.facebook.react.uimanager.BackgroundStyleApplicator
 import com.facebook.react.uimanager.HasChildPressedStateDelay
 import com.facebook.react.uimanager.LengthPercentage
@@ -169,6 +171,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
   private var disableIntervalMomentum = false
   private var snapInterval = 0
   private var snapOffsets: List<Int>? = null
+  private var sharedSnapOffsets: ScrollSnapOffsets? = null
   private var snapToStart = true
   private var snapToEnd = true
   private var snapToAlignment = SNAP_ALIGNMENT_DISABLED
@@ -277,6 +280,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
     disableIntervalMomentum = false
     snapInterval = 0
     snapOffsets = null
+    sharedSnapOffsets = null
     snapToStart = true
     snapToEnd = true
     snapToAlignment = SNAP_ALIGNMENT_DISABLED
@@ -388,6 +392,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
 
   public open fun setSnapOffsets(snapOffsets: List<Int>?) {
     this.snapOffsets = snapOffsets
+    sharedSnapOffsets = snapOffsets?.let { ScrollSnapOffsets.fromIntegerOffsets(it) }
   }
 
   public open fun setSnapToStart(snapToStart: Boolean) {
@@ -1223,8 +1228,8 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
 
     var smallerOffset = 0
     var largerOffset = maximumOffset
-    var firstOffset = 0
-    var lastOffset = maximumOffset
+    val firstOffset = 0
+    val lastOffset = maximumOffset
     val viewportWidth = width - paddingStart - paddingEnd
 
     // offsets are from the right edge in RTL layouts
@@ -1233,26 +1238,21 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
       velocityX = -velocityX
     }
 
-    // get the nearest snap points to the target offset
-    val offsets = snapOffsets
-    if (!offsets.isNullOrEmpty()) {
-      firstOffset = offsets[0]
-      lastOffset = offsets[offsets.size - 1]
-
-      for (i in offsets.indices) {
-        val offset = offsets[i]
-        if (offset <= targetOffset) {
-          if (targetOffset - offset < targetOffset - smallerOffset) {
-            smallerOffset = offset
-          }
-        }
-        if (offset >= targetOffset) {
-          if (offset - targetOffset < largerOffset - targetOffset) {
-            largerOffset = offset
-          }
-        }
-      }
-    } else if (snapToAlignment != SNAP_ALIGNMENT_DISABLED) {
+    val snapResult =
+        sharedSnapOffsets
+            ?.takeIf { !snapOffsets.isNullOrEmpty() }
+            ?.resolve(
+                currentOffset =
+                    (if (layoutDirection == LAYOUT_DIRECTION_RTL) maximumOffset - scrollX
+                        else scrollX)
+                        .toDouble(),
+                targetOffset = targetOffset.toDouble(),
+                maximumOffset = maximumOffset.toDouble(),
+                velocity = velocityX.toDouble(),
+                snapToStart = snapToStart,
+                snapToEnd = snapToEnd,
+            )
+    if (snapResult == null && snapToAlignment != SNAP_ALIGNMENT_DISABLED) {
       if (snapInterval > 0) {
         val ratio = targetOffset.toDouble() / snapInterval
         smallerOffset =
@@ -1303,7 +1303,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
         smallerOffset = max(smallerOffset, smallerChildOffset)
         largerOffset = kotlin.math.min(largerOffset, largerChildOffset)
       }
-    } else {
+    } else if (snapResult == null) {
       val interval = getSnapInterval().toDouble()
       val ratio = targetOffset.toDouble() / interval
       smallerOffset = (floor(ratio) * interval).toInt()
@@ -1321,7 +1321,18 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
     if (layoutDirection == LAYOUT_DIRECTION_RTL) {
       currentOffset = maximumOffset - currentOffset
     }
-    if (!snapToEnd && targetOffset >= lastOffset) {
+    if (snapResult != null) {
+      if (!hasCustomizedFlingAnimator) {
+        when (snapResult.direction) {
+          ScrollSnapDirection.FORWARD ->
+              velocityX += ((snapResult.selectedOffset.toInt() - targetOffset) * 10.0).toInt()
+          ScrollSnapDirection.BACKWARD ->
+              velocityX -= ((targetOffset - snapResult.selectedOffset.toInt()) * 10.0).toInt()
+          ScrollSnapDirection.NONE -> {}
+        }
+      }
+      targetOffset = snapResult.targetOffset.toInt()
+    } else if (!snapToEnd && targetOffset >= lastOffset) {
       if (currentOffset >= lastOffset) {
         // free scrolling
       } else {
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactNestedScrollView.kt b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactNestedScrollView.kt
index 45fee3cd19d1..b77233a0af61 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactNestedScrollView.kt
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactNestedScrollView.kt
@@ -37,6 +37,8 @@ import com.facebook.react.R
 import com.facebook.react.bridge.ReadableMap
 import com.facebook.react.common.ReactConstants
 import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags
+import com.facebook.react.shared.ScrollSnapDirection
+import com.facebook.react.shared.ScrollSnapOffsets
 import com.facebook.react.uimanager.BackgroundStyleApplicator
 import com.facebook.react.uimanager.HasChildPressedStateDelay
 import com.facebook.react.uimanager.LengthPercentage
@@ -203,6 +205,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
   private var disableIntervalMomentum = false
   private var snapInterval = 0
   private var snapOffsets: List<Int>? = null
+  private var sharedSnapOffsets: ScrollSnapOffsets? = null
   private var snapToStart = true
   private var snapToEnd = true
   private var snapToAlignment = SNAP_ALIGNMENT_DISABLED
@@ -252,6 +255,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
     disableIntervalMomentum = false
     snapInterval = 0
     snapOffsets = null
+    sharedSnapOffsets = null
     snapToStart = true
     snapToEnd = true
     snapToAlignment = SNAP_ALIGNMENT_DISABLED
@@ -359,6 +363,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
 
   open fun setSnapOffsets(snapOffsets: List<Int>?) {
     this.snapOffsets = snapOffsets
+    sharedSnapOffsets = snapOffsets?.let { ScrollSnapOffsets.fromIntegerOffsets(it) }
   }
 
   open fun setSnapToStart(snapToStart: Boolean) {
@@ -923,29 +928,20 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
 
     var smallerOffset = 0
     var largerOffset = maximumOffset
-    var firstOffset = 0
-    var lastOffset = maximumOffset
+    val firstOffset = 0
+    val lastOffset = maximumOffset
     val viewportHeight = height - paddingBottom - paddingTop
 
-    val currentSnapOffsets = snapOffsets
-    if (currentSnapOffsets != null) {
-      firstOffset = currentSnapOffsets[0]
-      lastOffset = currentSnapOffsets[currentSnapOffsets.size - 1]
-
-      for (i in currentSnapOffsets.indices) {
-        val offset = currentSnapOffsets[i]
-        if (offset <= targetOffset) {
-          if (targetOffset - offset < targetOffset - smallerOffset) {
-            smallerOffset = offset
-          }
-        }
-        if (offset >= targetOffset) {
-          if (offset - targetOffset < largerOffset - targetOffset) {
-            largerOffset = offset
-          }
-        }
-      }
-    } else if (snapToAlignment != SNAP_ALIGNMENT_DISABLED) {
+    val snapResult =
+        sharedSnapOffsets?.resolve(
+            currentOffset = scrollY.toDouble(),
+            targetOffset = targetOffset.toDouble(),
+            maximumOffset = maximumOffset.toDouble(),
+            velocity = velocityY.toDouble(),
+            snapToStart = snapToStart,
+            snapToEnd = snapToEnd,
+        )
+    if (snapResult == null && snapToAlignment != SNAP_ALIGNMENT_DISABLED) {
       if (snapInterval > 0) {
         val ratio = targetOffset.toDouble() / snapInterval
         smallerOffset =
@@ -998,7 +994,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
         smallerOffset = max(smallerOffset, smallerChildOffset)
         largerOffset = min(largerOffset, largerChildOffset)
       }
-    } else {
+    } else if (snapResult == null) {
       val interval = getSnapInterval().toDouble()
       val ratio = targetOffset.toDouble() / interval
       smallerOffset = (floor(ratio) * interval).toInt()
@@ -1009,7 +1005,18 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
         if (abs(targetOffset - smallerOffset) < abs(largerOffset - targetOffset)) smallerOffset
         else largerOffset
 
-    if (!snapToEnd && targetOffset >= lastOffset) {
+    if (snapResult != null) {
+      if (!hasCustomizedFlingAnimator) {
+        when (snapResult.direction) {
+          ScrollSnapDirection.FORWARD ->
+              velocityY += ((snapResult.selectedOffset.toInt() - targetOffset) * 10.0).toInt()
+          ScrollSnapDirection.BACKWARD ->
+              velocityY -= ((targetOffset - snapResult.selectedOffset.toInt()) * 10.0).toInt()
+          ScrollSnapDirection.NONE -> {}
+        }
+      }
+      targetOffset = snapResult.targetOffset.toInt()
+    } else if (!snapToEnd && targetOffset >= lastOffset) {
       if (scrollY >= lastOffset) {
         // free scrolling
       } else {
diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.kt b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.kt
index b553f6af997d..1454fd3a7b99 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.kt
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.kt
@@ -29,6 +29,8 @@ import com.facebook.react.R
 import com.facebook.react.bridge.ReadableMap
 import com.facebook.react.common.ReactConstants
 import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags
+import com.facebook.react.shared.ScrollSnapDirection
+import com.facebook.react.shared.ScrollSnapOffsets
 import com.facebook.react.uimanager.BackgroundStyleApplicator
 import com.facebook.react.uimanager.HasChildPressedStateDelay
 import com.facebook.react.uimanager.LengthPercentage
@@ -195,6 +197,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
   private var disableIntervalMomentum = false
   private var snapInterval = 0
   private var snapOffsets: List<Int>? = null
+  private var sharedSnapOffsets: ScrollSnapOffsets? = null
   private var snapToStart = true
   private var snapToEnd = true
   private var snapToAlignment = SNAP_ALIGNMENT_DISABLED
@@ -244,6 +247,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
     disableIntervalMomentum = false
     snapInterval = 0
     snapOffsets = null
+    sharedSnapOffsets = null
     snapToStart = true
     snapToEnd = true
     snapToAlignment = SNAP_ALIGNMENT_DISABLED
@@ -351,6 +355,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
 
   public open fun setSnapOffsets(snapOffsets: List<Int>?) {
     this.snapOffsets = snapOffsets
+    sharedSnapOffsets = snapOffsets?.let { ScrollSnapOffsets.fromIntegerOffsets(it) }
   }
 
   public open fun setSnapToStart(snapToStart: Boolean) {
@@ -915,29 +920,20 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
 
     var smallerOffset = 0
     var largerOffset = maximumOffset
-    var firstOffset = 0
-    var lastOffset = maximumOffset
+    val firstOffset = 0
+    val lastOffset = maximumOffset
     val viewportHeight = height - paddingBottom - paddingTop
 
-    val currentSnapOffsets = snapOffsets
-    if (currentSnapOffsets != null) {
-      firstOffset = currentSnapOffsets[0]
-      lastOffset = currentSnapOffsets[currentSnapOffsets.size - 1]
-
-      for (i in currentSnapOffsets.indices) {
-        val offset = currentSnapOffsets[i]
-        if (offset <= targetOffset) {
-          if (targetOffset - offset < targetOffset - smallerOffset) {
-            smallerOffset = offset
-          }
-        }
-        if (offset >= targetOffset) {
-          if (offset - targetOffset < largerOffset - targetOffset) {
-            largerOffset = offset
-          }
-        }
-      }
-    } else if (snapToAlignment != SNAP_ALIGNMENT_DISABLED) {
+    val snapResult =
+        sharedSnapOffsets?.resolve(
+            currentOffset = scrollY.toDouble(),
+            targetOffset = targetOffset.toDouble(),
+            maximumOffset = maximumOffset.toDouble(),
+            velocity = velocityY.toDouble(),
+            snapToStart = snapToStart,
+            snapToEnd = snapToEnd,
+        )
+    if (snapResult == null && snapToAlignment != SNAP_ALIGNMENT_DISABLED) {
       if (snapInterval > 0) {
         val ratio = targetOffset.toDouble() / snapInterval
         smallerOffset =
@@ -990,7 +986,7 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
         smallerOffset = max(smallerOffset, smallerChildOffset)
         largerOffset = min(largerOffset, largerChildOffset)
       }
-    } else {
+    } else if (snapResult == null) {
       val interval = getSnapInterval().toDouble()
       val ratio = targetOffset.toDouble() / interval
       smallerOffset = (floor(ratio) * interval).toInt()
@@ -1001,7 +997,18 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
         if (abs(targetOffset - smallerOffset) < abs(largerOffset - targetOffset)) smallerOffset
         else largerOffset
 
-    if (!snapToEnd && targetOffset >= lastOffset) {
+    if (snapResult != null) {
+      if (!hasCustomizedFlingAnimator) {
+        when (snapResult.direction) {
+          ScrollSnapDirection.FORWARD ->
+              velocityY += ((snapResult.selectedOffset.toInt() - targetOffset) * 10.0).toInt()
+          ScrollSnapDirection.BACKWARD ->
+              velocityY -= ((targetOffset - snapResult.selectedOffset.toInt()) * 10.0).toInt()
+          ScrollSnapDirection.NONE -> {}
+        }
+      }
+      targetOffset = snapResult.targetOffset.toInt()
+    } else if (!snapToEnd && targetOffset >= lastOffset) {
       if (scrollY >= lastOffset) {
         // free scrolling
       } else {
diff --git a/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt
index 1ef4499184aa..84d227da0fa3 100644
--- a/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt
+++ b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt
@@ -10,6 +10,8 @@ package com.facebook.react.devsupport
 import okio.Buffer
 import okio.BufferedSource
 import okio.ByteString
+import okio.ForwardingSource
+import okio.Okio
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.Test
 
@@ -212,6 +214,93 @@ class MultipartStreamReaderTest {
     assertThat(callback.callCount).isEqualTo(1)
   }
 
+  @Test
+  @Suppress("DEPRECATION_ERROR") // Match the reader's compatibility with legacy Okio.
+  fun testDelimitersAcrossEveryReadBoundary() {
+    // The trailing CRLF must not become a header separator spanning the next boundary.
+    val body = "binary\u0000\r\n--samplX\r\n--sample-\r\n"
+    val response = "preamble\r\n--sample\r\n${body}\r\n--sample\r\nsecond\r\n--sample--\r\nepilogue"
+    for (readSize in 1..response.length) {
+      val upstream = Buffer().writeUtf8(response)
+      val source =
+          Okio.buffer(
+              object : ForwardingSource(upstream) {
+                override fun read(sink: Buffer, byteCount: Long): Long =
+                    super.read(sink, minOf(byteCount, readSize.toLong()))
+              }
+          )
+      val parts = mutableListOf<String>()
+      val last = mutableListOf<Boolean>()
+      val success =
+          MultipartStreamReader(source, "sample")
+              .readAllParts(
+                  object : CallCountTrackingChunkCallback() {
+                    override fun onChunkComplete(
+                        headers: Map<String, String>,
+                        body: BufferedSource,
+                        isLastChunk: Boolean,
+                    ) {
+                      parts.add(body.readUtf8())
+                      last.add(isLastChunk)
+                    }
+                  }
+              )
+      assertThat(success).describedAs("read size %s", readSize).isTrue()
+      assertThat(parts).containsExactly(body, "second")
+      assertThat(last).containsExactly(false, true)
+    }
+  }
+
+  @Test
+  fun testHeaderWhitespaceDuplicatesAndColonValues() {
+    val source =
+        Buffer()
+            .writeUtf8(
+                "\r\n--sample\r\n X-Name : first\r\nx-name: second:extra \r\ninvalid\r\n\r\nbody\r\n--sample--\r\n"
+            )
+    var calls = 0
+    assertThat(
+            MultipartStreamReader(source, "sample")
+                .readAllParts(
+                    object : CallCountTrackingChunkCallback() {
+                      override fun onChunkComplete(
+                          headers: Map<String, String>,
+                          body: BufferedSource,
+                          isLastChunk: Boolean,
+                      ) {
+                        calls++
+                        assertThat(headers).hasSize(1)
+                        assertThat(headers["X-Name"]).isEqualTo("second:extra")
+                        assertThat(body.readUtf8()).isEqualTo("body")
+                        assertThat(isLastChunk).isTrue()
+                      }
+                    }
+                )
+        )
+        .isTrue()
+    assertThat(calls).isEqualTo(1)
+  }
+
+  @Test
+  fun testFinalProgressForFragmentedBody() {
+    val body = "x".repeat(64 * 1024)
+    val source =
+        Buffer()
+            .writeUtf8(
+                "\r\n--sample\r\nContent-Length: ${body.length}\r\n\r\n$body\r\n--sample--\r\n"
+            )
+    val progress = mutableListOf<Pair<Long, Long>>()
+    val callback =
+        object : CallCountTrackingChunkCallback() {
+          override fun onChunkProgress(headers: Map<String, String>, loaded: Long, total: Long) {
+            progress.add(loaded to total)
+          }
+        }
+    assertThat(MultipartStreamReader(source, "sample").readAllParts(callback)).isTrue()
+    assertThat(callback.callCount).isEqualTo(1)
+    assertThat(progress.last()).isEqualTo(body.length.toLong() to body.length.toLong())
+  }
+
   internal open class CallCountTrackingChunkCallback : MultipartStreamReader.ChunkListener {
     var callCount = 0
       private set
diff --git a/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/style/ColorStopTest.kt b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/style/ColorStopTest.kt
index 005b0bf6d4c6..fa89503d22fc 100644
--- a/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/style/ColorStopTest.kt
+++ b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/uimanager/style/ColorStopTest.kt
@@ -176,4 +176,90 @@ class ColorStopTest {
     assertThat(processed[4].color).isEqualTo(Color.MAGENTA)
     assertThat(processed[4].position).isEqualTo(1f)
   }
+
+  @Test
+  fun testPointPositionsUseAndroidDisplayDensityBeforeSharedFixup() {
+    val metrics = DisplayMetrics()
+    metrics.density = 2f
+    DisplayMetricsHolder.setScreenDisplayMetrics(metrics)
+    val colorStops =
+        listOf(
+            ColorStop(Color.RED, LengthPercentage(25f, LengthPercentageType.POINT)),
+            ColorStop(Color.BLUE, LengthPercentage(100f, LengthPercentageType.PERCENT)),
+        )
+
+    val processed = ColorStopUtils.getFixedColorStops(colorStops, 200f)
+
+    assertThat(processed[0].position).isEqualTo(.25f)
+    assertThat(processed[1].position).isEqualTo(1f)
+  }
+
+  @Test
+  fun testTransitionHintKeepsAndroidColorAndAlphaRounding() {
+    val colorStops =
+        listOf(
+            ColorStop(Color.argb(128, 255, 0, 0)),
+            ColorStop(null, LengthPercentage(25f, LengthPercentageType.PERCENT)),
+            ColorStop(Color.BLUE),
+        )
+
+    val processed = ColorStopUtils.getFixedColorStops(colorStops, 100f)
+
+    assertThat(processed).hasSize(11)
+    assertThat(processed[3].position).isEqualTo(.25f)
+    assertThat(processed[3].color).isEqualTo(Color.argb(191, 127, 0, 127))
+    assertThat(processed.first().color).isEqualTo(Color.argb(128, 255, 0, 0))
+    assertThat(processed.last().color).isEqualTo(Color.BLUE)
+  }
+
+  @Test
+  fun testEndpointHintsReuseTheOppositeColorWithoutBlending() {
+    for ((hintPosition, expectedColor) in listOf(0f to Color.BLUE, 100f to Color.RED)) {
+      val colorStops =
+          listOf(
+              ColorStop(Color.RED),
+              ColorStop(null, LengthPercentage(hintPosition, LengthPercentageType.PERCENT)),
+              ColorStop(Color.BLUE),
+          )
+
+      val processed = ColorStopUtils.getFixedColorStops(colorStops, 100f)
+
+      assertThat(processed).hasSize(3)
+      assertThat(processed[1].color).isEqualTo(expectedColor)
+      assertThat(processed[1].position).isEqualTo(hintPosition / 100f)
+    }
+  }
+
+  @Test
+  fun testCenteredHintDoesNotChangeTheColors() {
+    val colorStops =
+        listOf(
+            ColorStop(Color.RED),
+            ColorStop(null, LengthPercentage(50f, LengthPercentageType.PERCENT)),
+            ColorStop(Color.BLUE),
+        )
+
+    val processed = ColorStopUtils.getFixedColorStops(colorStops, 100f)
+
+    assertThat(processed).hasSize(2)
+    assertThat(processed[0].color).isEqualTo(Color.RED)
+    assertThat(processed[1].color).isEqualTo(Color.BLUE)
+  }
+
+  @Test
+  fun testZeroLengthGradientKeepsNonFiniteSamplesUncolored() {
+    val colorStops =
+        listOf(
+            ColorStop(Color.RED),
+            ColorStop(null, LengthPercentage(10f, LengthPercentageType.POINT)),
+            ColorStop(Color.BLUE, LengthPercentage(20f, LengthPercentageType.POINT)),
+        )
+
+    val processed = ColorStopUtils.getFixedColorStops(colorStops, 0f)
+
+    assertThat(processed).hasSize(11)
+    assertThat(processed.first().color).isEqualTo(Color.RED)
+    assertThat(processed.last().color).isEqualTo(Color.BLUE)
+    assertThat(processed.subList(1, 10).all { it.color == null }).isTrue()
+  }
 }
diff --git a/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/scroll/ReactScrollSnapOffsetsTest.kt b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/scroll/ReactScrollSnapOffsetsTest.kt
new file mode 100644
index 000000000000..a837024b9b0e
--- /dev/null
+++ b/packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/scroll/ReactScrollSnapOffsetsTest.kt
@@ -0,0 +1,295 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.views.scroll
+
+import android.animation.ValueAnimator
+import android.graphics.Point
+import android.view.View
+import android.view.ViewGroup
+import android.widget.OverScroller
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlagsForTests
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertThrows
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.MockedStatic
+import org.mockito.Mockito
+import org.mockito.stubbing.Answer
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/** Exercises the real flingAndSnap methods while recording their native physics calls. */
+@RunWith(RobolectricTestRunner::class)
+@Config(manifest = Config.NONE, sdk = [28])
+class ReactScrollSnapOffsetsTest {
+  private val drivers = mutableListOf<ScrollSnapTestDriver>()
+  private lateinit var helper: MockedStatic<ReactScrollViewHelper>
+
+  @Before
+  fun setUp() {
+    ReactNativeFeatureFlagsForTests.setUp()
+    helper =
+        Mockito.mockStatic(
+            ReactScrollViewHelper::class.java,
+            Answer { invocation ->
+              if (invocation.method.name == "predictFinalScrollPosition") {
+                val driver = drivers.single { it.view === invocation.arguments[0] }
+                if (driver.horizontal) Point(driver.predicted, 0) else Point(0, driver.predicted)
+              } else {
+                invocation.callRealMethod()
+              }
+            },
+        )
+  }
+
+  @After
+  fun tearDown() {
+    helper.close()
+  }
+
+  private fun eachView(block: (ScrollSnapTestDriver) -> Unit) {
+    for (name in listOf("ReactScrollView", "ReactNestedScrollView", "ReactHorizontalScrollView")) {
+      val driver = ScrollSnapTestDriver(name)
+      drivers.add(driver)
+      block(driver)
+    }
+  }
+
+  @Test
+  fun explicitOffsetsPreserveNativeVelocityBoost() = eachView { driver ->
+    driver.setOffsets(listOf(20, 60, 100))
+    driver.predicted = 40
+    assertEquals(ScrollSnapObservation(60, 210, 0), driver.fling(10))
+    assertEquals(ScrollSnapObservation(20, -210, 0), driver.fling(-10))
+    assertEquals(ScrollSnapObservation(60, 60, 0), driver.fling(0))
+  }
+
+  @Test
+  fun customizedAnimatorReceivesOnlyTheSelectedTarget() = eachView { driver ->
+    driver.customAnimator = true
+    driver.setOffsets(listOf(20, 60, 100))
+    driver.predicted = 40
+    assertEquals(ScrollSnapObservation(60, null, null), driver.fling(10))
+    assertEquals(ScrollSnapObservation(20, null, null), driver.fling(-10))
+  }
+
+  @Test
+  fun disabledBoundariesPreserveFreeScrollingAndCrossing() = eachView { driver ->
+    driver.setOffsets(listOf(20, 60, 100))
+    driver.set("setSnapToStart", false)
+    driver.set("setSnapToEnd", false)
+    driver.current = 110
+    driver.predicted = 120
+    assertEquals(ScrollSnapObservation(120, 10, 0), driver.fling(10))
+    driver.current = 90
+    assertEquals(ScrollSnapObservation(100, 10, 0), driver.fling(10))
+    driver.current = 10
+    driver.predicted = 0
+    assertEquals(ScrollSnapObservation(0, -10, 100), driver.fling(-10))
+    driver.current = 30
+    assertEquals(ScrollSnapObservation(20, -10, 0), driver.fling(-10))
+  }
+
+  @Test
+  fun disablingMomentumUsesCurrentOffsetBeforeSelecting() = eachView { driver ->
+    driver.setOffsets(listOf(20, 60, 100))
+    driver.set("setDisableIntervalMomentum", true)
+    driver.current = 25
+    driver.predicted = 90
+    assertEquals(ScrollSnapObservation(60, 360, 0), driver.fling(10))
+  }
+
+  @Test
+  fun propertyChangesAndNativeMutationsRemainVisible() = eachView { driver ->
+    driver.customAnimator = true
+    val offsets = mutableListOf(20, 60, 100)
+    driver.setOffsets(offsets)
+    driver.predicted = 40
+    offsets[1] = 90
+    assertEquals(90, driver.fling(10).target)
+    offsets.add(50)
+    assertEquals(50, driver.fling(10).target)
+    driver.setOffsets(listOf(20, 80, 100))
+    assertEquals(80, driver.fling(10).target)
+    driver.setOffsets(null)
+    driver.set("setSnapInterval", 50)
+    assertEquals(50, driver.fling(10).target)
+  }
+
+  @Test
+  fun clearingRetainedListsPreservesPlatformEmptyListBehavior() = eachView { driver ->
+    val offsets = mutableListOf(20, 60, 100)
+    driver.setOffsets(offsets)
+    driver.set("setSnapInterval", 50)
+    driver.predicted = 40
+    offsets.clear()
+    if (driver.horizontal) {
+      assertEquals(50, driver.fling(10).target)
+    } else {
+      val failure =
+          assertThrows(java.lang.reflect.InvocationTargetException::class.java) { driver.fling(10) }
+      assertTrue(failure.cause is IndexOutOfBoundsException)
+    }
+  }
+
+  @Test
+  fun recyclingClearsTheSelectorBeforeNativeIntervalSnapping() = eachView { driver ->
+    driver.setOffsets(listOf(20, 60, 100))
+    driver.recycle()
+    driver.set("setSnapInterval", 50)
+    driver.predicted = 40
+    assertEquals(50, driver.fling(10).target)
+  }
+
+  @Test
+  fun extremeOffsetsPreserveAndroidIntegerArithmetic() = eachView { driver ->
+    driver.setOffsets(listOf(Int.MIN_VALUE, 20, 100))
+    driver.predicted = 150
+    assertEquals(ScrollSnapObservation(300, 300, 100), driver.fling(0))
+  }
+
+  @Test
+  fun horizontalRtlKeepsCoordinatesAndVelocityInNativeSpace() {
+    val driver = ScrollSnapTestDriver("ReactHorizontalScrollView")
+    drivers.add(driver)
+    driver.rtl = true
+    driver.current = 280
+    driver.predicted = 260
+    driver.setOffsets(listOf(20, 60, 100))
+    assertEquals(ScrollSnapObservation(240, -210, 0), driver.fling(-10))
+    assertEquals(ScrollSnapObservation(280, 210, 0), driver.fling(10))
+  }
+}
+
+internal data class ScrollSnapObservation(val target: Int, val velocity: Int?, val overscroll: Int?)
+
+/**
+ * Native prediction/rendering are controlled; selection and velocity adjustment execute unchanged.
+ */
+internal class ScrollSnapTestDriver(name: String) {
+  val horizontal = name.contains("Horizontal")
+  var current = 0
+  var predicted = 0
+  var maximum = 300
+  var rtl = false
+  var customAnimator = false
+  private var observation: ScrollSnapObservation? = null
+  private val type =
+      Class.forName("com.facebook.react.views.scroll.$name").asSubclass(ViewGroup::class.java)
+  private val defaultAnimator = Mockito.mock(ValueAnimator::class.java)
+  private val otherAnimator = Mockito.mock(ValueAnimator::class.java)
+  private val state = ReactScrollViewHelper.ReactScrollViewScrollState().apply { isFinished = true }
+  private val child =
+      Mockito.mock(
+          View::class.java,
+          Answer { invocation ->
+            when (invocation.method.name) {
+              "getHeight",
+              "getWidth",
+              "getBottom",
+              "getRight" -> maximum + 200
+              else -> Mockito.RETURNS_DEFAULTS.answer(invocation)
+            }
+          },
+      )
+  private val scroller =
+      Mockito.mock(
+          OverScroller::class.java,
+          Answer { invocation ->
+            if (invocation.method.name == "fling") {
+              val args = invocation.arguments
+              observation =
+                  ScrollSnapObservation(
+                      args[if (horizontal) 4 else 6] as Int,
+                      args[if (horizontal) 2 else 3] as Int,
+                      args[if (horizontal) 8 else 9] as Int,
+                  )
+              null
+            } else {
+              Mockito.RETURNS_DEFAULTS.answer(invocation)
+            }
+          },
+      )
+  val view: ViewGroup =
+      Mockito.mock(
+          type,
+          Answer { invocation ->
+            when (invocation.method.name) {
+              "getFlingAnimator" -> if (customAnimator) otherAnimator else defaultAnimator
+              "getFlingExtrapolatedDistance" -> predicted - current
+              "getReactScrollViewScrollState" -> state
+              "getScrollX" -> if (horizontal) current else 0
+              "getScrollY" -> if (horizontal) 0 else current
+              "getWidth",
+              "getHeight" -> 200
+              "computeHorizontalScrollRange" -> maximum + 200
+              "getPaddingStart",
+              "getPaddingEnd",
+              "getPaddingTop",
+              "getPaddingBottom" -> 0
+              "getChildCount" -> 1
+              "getChildAt" -> child
+              "getLayoutDirection" ->
+                  if (rtl) View.LAYOUT_DIRECTION_RTL else View.LAYOUT_DIRECTION_LTR
+              "postInvalidateOnAnimation", "invalidate" -> null
+              "reactSmoothScrollTo" -> {
+                observation =
+                    ScrollSnapObservation(
+                        invocation.arguments[if (horizontal) 0 else 1] as Int,
+                        null,
+                        null,
+                    )
+                null
+              }
+              else -> invocation.callRealMethod()
+            }
+          },
+      )
+
+  init {
+    for ((name, value) in
+        listOf(
+            "defaultFlingAnimator" to defaultAnimator,
+            "scroller" to scroller,
+            "contentView" to child,
+        )) {
+      type.declaredFields.find { it.name == name }?.apply { isAccessible = true }?.set(view, value)
+    }
+    set("setSnapToStart", true)
+    set("setSnapToEnd", true)
+  }
+
+  fun set(name: String, value: Any) {
+    type.methods.single { it.name == name && it.parameterCount == 1 }.invoke(view, value)
+  }
+
+  fun setOffsets(offsets: List<Int>?) {
+    type.getMethod("setSnapOffsets", List::class.java).invoke(view, offsets)
+  }
+
+  fun recycle() {
+    type.declaredMethods
+        .single { it.name.startsWith("recycleView") }
+        .apply { isAccessible = true }
+        .invoke(view)
+    // Reattach the fixture's measured content after the real recycle reset.
+    type.getMethod("onChildViewAdded", View::class.java, View::class.java).invoke(view, view, child)
+  }
+
+  fun fling(velocity: Int): ScrollSnapObservation {
+    observation = null
+    type
+        .getDeclaredMethod("flingAndSnap", Int::class.javaPrimitiveType)
+        .apply { isAccessible = true }
+        .invoke(view, velocity)
+    return checkNotNull(observation)
+  }
+}
diff --git a/packages/react-native/ReactShared/.gitignore b/packages/react-native/ReactShared/.gitignore
new file mode 100644
index 000000000000..5d8581f71fc8
--- /dev/null
+++ b/packages/react-native/ReactShared/.gitignore
@@ -0,0 +1,3 @@
+/build/
+/.gradle/
+/.kotlin/
diff --git a/packages/react-native/ReactShared/README.md b/packages/react-native/ReactShared/README.md
new file mode 100644
index 000000000000..12051499206b
--- /dev/null
+++ b/packages/react-native/ReactShared/README.md
@@ -0,0 +1,229 @@
+# React Native shared Kotlin experiments
+
+These use cases build on the standalone KMP foundation. The
+foundation's unpublished compiler/interop fixture remains available with
+`-PreactNativeSharedSmoke=true`; its classes and reports stay under
+`build/smoke` and are excluded from normal shared outputs. Run
+`./scripts/test-apple-smoke.sh` to check that fixture through Objective-C.
+Each use case has a separate behavior and performance review.
+
+This module shares CSS gradient stop position and transition-hint calculations
+between Android and iOS using Kotlin Multiplatform. It has no Compose dependency.
+Native views, gradient geometry, color interpolation, and drawing remain in their
+existing platform implementations.
+
+`commonMain` accepts positions and color-presence flags and returns positions,
+source color indices, and interpolation weights. Platform adapters retain their
+existing tolerance, logarithm precision, and color-space behavior. The module does
+not depend on ReactAndroid, React-Core, UIKit, JNI, or the C++ renderer.
+
+## Multipart framing
+
+`MultipartFraming` shares delimiter overlap, preamble and completed-part state
+between Android's sliding Okio buffer and Apple's retained NSData buffer.
+`MultipartHeaders` splits raw header fields; each platform keeps its existing
+whitespace and key-comparison rules. Native code retains buffer searches, stream
+and body ownership, callbacks and progress timing. Body bytes never cross the
+Kotlin/Objective-C boundary.
+
+Run `./scripts/test-apple-multipart.sh` and
+`python3 scripts/test-android-multipart.py` for the actual adapters' tests from a
+repository checkout; their Android and RNTester test sources are not distributed
+in the npm package. The Android runner requires Python 3.11 or later and uses the
+repository's Okio, AssertJ, JUnit and Kotlin standard-library versions. Its newer
+standalone compiler retains ReactAndroid's Kotlin language and API level.
+The Apple runner also compares exact callbacks/body bytes against the native
+fallback and checks Catalyst. Set `RCT_KMP_BENCHMARK=1` for its optional 2–20 MiB
+parser benchmark. The Android runner supports `--baseline-ref` with an explicit
+native parser revision and `--benchmark`; see `--help`. Its timings and allocation
+counters describe a host JVM, not Android ART or network download throughput.
+Both probes exclude constructing their known input payloads.
+
+This use case can amortize interop over buffer reads. A C++ implementation could
+also share decisions and directly search native buffers, but would add an Android
+JNI interface to this currently Kotlin/Objective-C utility. Neither approach
+removes platform I/O or Catalyst fallback. Measure application memory and real
+bundle-download behavior before broadening adoption.
+
+## Explicit scroll offsets
+
+`ScrollSnapOffsets` selects a target from explicit offsets for three Android views
+and Apple's enhanced scroll view. Target prediction, axis/RTL handling, density,
+velocity adjustment, interval snapping and native physics remain in the views.
+Android retains its caller-owned integer list and pixel arithmetic. Apple caches
+a primitive offset array when the property changes, then calls the selector once
+per fling. It does not call Kotlin on every animation frame.
+
+`python3 scripts/test-apple-scroll-snap.py --benchmark-repeats 0` compiles the
+actual Apple view with native and KMP paths, checks their target outputs, and
+checks Catalyst fallback. The runner also compiles a test-only cached native
+control to separate storage/caching benefits from Kotlin's contribution.
+Omit that option to collect timing samples; the framework includes all use cases
+present in the checkout. The Android core test suite includes
+`ReactScrollSnapOffsetsTest`, which exercises all three views' actual fling code.
+
+This is a Kotlin-first consumer with a small target/direction result on Apple. A shared
+C++ selector or caching the native Apple offsets are both alternatives; faster
+results against the original NSNumber loop alone would not establish a KMP
+advantage. Evaluate first-use cost, offset updates and repeated calls separately.
+
+## Build and test
+
+The standalone build uses its own Gradle wrapper and Kotlin plugin so that it
+does not change the Kotlin plugin used by the main Android build. It requires
+JDK 17. Apple builds also require macOS and Xcode; the pilot CI selects Xcode
+26.4.1 without changing the existing React Native CI toolchain.
+
+From this directory:
+
+```sh
+./gradlew jvmTest
+./gradlew iosSimulatorArm64Test
+./gradlew linkDebugFrameworkIosArm64 linkReleaseFrameworkIosArm64 \
+  linkDebugFrameworkIosSimulatorArm64 linkReleaseFrameworkIosSimulatorArm64 \
+  linkDebugFrameworkIosX64 linkReleaseFrameworkIosX64
+./scripts/test-apple-gradient.sh
+RCT_KMP_BUILD_TYPE=Release ./scripts/test-apple-gradient.sh
+```
+
+The same common tests run on JVM and the Apple Silicon iOS simulator. The build
+also defines an `iosX64` target for Intel simulators. Device and simulator
+frameworks are static and named `ReactNativeShared.framework`. The Apple parity
+script requires an installed iOS simulator runtime and compares the actual
+Objective-C++ adapter with the existing native gradient implementation.
+
+With CocoaPods installed, `bundle exec ruby scripts/test-cocoapods-linking.rb`
+checks generated host and test configurations for static, dynamic, and mixed
+per-target linkage. Local fixture pods cover inherited and full-pod sibling hosted
+tests, with and without `TestTargetID`, including renamed and SDK-specific app products. Negative
+controls cover standalone tests and non-KMP hosts with unrelated KMP app dependencies.
+No native code is compiled; the check verifies framework search paths and expected
+Kotlin archive links, then prints the generated configuration directory.
+Host paths with unresolved architecture or SDK-version conditions are not treated
+as proof that the app provides the Kotlin runtime; those configurations need explicit
+validation before relying on hosted-test suppression.
+
+## Android integration
+
+The repository and npm source-build settings include this directory as a
+separate Gradle build. ReactAndroid consumes its JVM output through
+`exportAndroidJar`, which writes `build/android/react-native-shared.jar`.
+ReactAndroid embeds that JAR in its existing AAR; consumers continue to use the
+existing `com.facebook.react:react-android` dependency.
+
+The JVM target uses Java 17 bytecode and Kotlin 2.2 language/API compatibility.
+Android-specific build variants, resources, CMake, JNI, and publication remain
+owned by ReactAndroid.
+
+`python3 scripts/test-android-consumers.py` publishes to a temporary local Maven
+repository, packs the npm sources, and builds a fresh Android application for
+each dependency route. It checks dependency resolution, shared-class uniqueness,
+Debug packaging and Release shrinking. See `--help` for emulator execution and
+fixture preparation options. These small consumers exercise the real Android
+gradient and multipart adapters; they do not replace RNTester coverage.
+
+## Apple opt-in
+
+The Apple adapter is a source-build pilot. Set the flag when installing Pods in
+the application directory that contains its Podfile:
+
+```sh
+RCT_USE_KMP=1 bundle exec pod install
+```
+
+This enables the `React-KMP` support pod and selects React Native core source
+builds. During the Xcode build, the support pod builds the shared static framework
+for the current SDK, architecture, and configuration. The application still uses
+its existing Objective-C++ and UIKit rendering code.
+
+All Apple consumers use one shared Kotlin runtime. With dynamic CocoaPods
+frameworks, `React-Core` owns the static Kotlin archive and exports its Objective-C
+classes to dependent pods such as Fabric. The archive is explicitly loaded so the
+owner does not depend on which shared algorithm it happens to call. With static
+libraries or static frameworks, the application owns the archive instead. Hosted
+tests inherit their host's runtime. Adding an algorithm must not add another
+framework link to its consuming pod.
+
+For a custom Xcode configuration name that does not contain `Debug` or `Release`,
+set the `RCT_KMP_BUILD_TYPE` build setting to `Debug` or `Release`.
+
+Mac Catalyst retains the existing gradient implementation because Kotlin/Native
+does not provide a Catalyst target. SwiftPM does not support this pilot: setting
+`RCT_USE_KMP=1` for that integration fails with a message directing developers to
+the CocoaPods source-build route. Published React Native Apple prebuilts do not
+contain the pilot framework.
+
+`./scripts/test-apple-distribution.sh` tests a separate binary-distribution
+fixture: a device ARM64 plus universal simulator XCFramework, the matching Kotlin
+license bundle, and a SwiftPM consumer. It builds iOS and Catalyst and executes
+the consumer's test on the host simulator. `--build-only` omits execution;
+`--package-only` packages previously built frameworks and records that reuse in
+`distribution.json`. This probe does not enable React Native core's SwiftPM or
+prebuilt integration. Those routes still need complete React core build and app
+validation before their guard can be removed.
+
+To return to the default Apple implementation, remove the flag and run Pod
+installation again. No change to the JavaScript gradient API is needed.
+
+## Application, runtime and cost checks
+
+From a repository checkout with RNTester dependencies installed:
+
+```sh
+./scripts/test-apple-app.sh simulator
+USE_FRAMEWORKS=static ./scripts/test-apple-app.sh simulator
+USE_FRAMEWORKS=dynamic ./scripts/test-apple-app.sh simulator
+./scripts/test-apple-app.sh device
+./scripts/test-apple-app.sh catalyst
+python3 scripts/test-kotlin-coexistence.py
+python3 scripts/benchmark-apple-gradient.py
+python3 scripts/benchmark-kmp-build.py
+```
+
+The app script copies RNTester into an isolated sibling directory, enables KMP,
+and verifies the actual compiled gradient, multipart and scroll adapters. Simulator runs
+execute the RNTester test plan and launch the app; device and Catalyst runs are unsigned
+build checks. Catalyst is enabled in the copied Podfile and application project.
+Each run requires fresh build outputs. It preserves RNTester's existing hosted-test topology and removes
+the temporary app and any test-owned servers and simulator when it finishes.
+
+The coexistence fixture checks independently compiled Kotlin frameworks using
+the same compiler as ReactShared, including all four combinations of static and dynamic runtime ownership,
+object lifetimes, and concurrent calls. Values cross that boundary as native
+primitives. It does not establish compatibility with arbitrary Kotlin compiler
+versions or allow one framework's exported Kotlin objects to be cast to another's.
+
+The Apple benchmark compares the actual native and KMP adapters in separate
+optimized executables. It records first-call and repeated-call timings, process
+memory snapshots and binary size. Memory snapshots are not allocation counts,
+and simulator measurements are not application startup or physical-device
+performance. The build benchmark measures clean outputs, unchanged builds and a
+common-source edit in a copied module with warm dependency/compiler caches and
+Gradle's build-output cache disabled. Reports have no timing pass/fail thresholds.
+Measure full application size, startup, allocations and build costs on representative
+devices before expanding adoption.
+
+This is an experimental code-sharing pilot. Local optimized simulator probes
+show additional latency, executable size and process memory cost from the shared
+adapter and Kotlin runtime. Passing correctness and integration tests does not
+establish an acceptable performance budget for broader adoption.
+
+## Scope and validation
+
+Common tests cover stop positioning and transition hints. They do not replace
+platform rendering tests: color precision, gradient geometry, and framework
+linking still need validation in the Android and Apple adapters. Adoption beyond
+this pilot should also measure application size and startup cost and preserve
+the existing Catalyst path.
+
+The dedicated `test-kmp.yml` workflow runs common tests, builds Debug and Release
+frameworks for all three Apple targets, and checks Apple adapter parity in both
+configurations with static and dynamic linkage. It also checks CocoaPods linking
+for application and test targets with static, dynamic, and mixed framework settings.
+Additional jobs cover KMP-enabled RNTester builds/tests and Android package consumers;
+the shared job runs the distribution, coexistence and cost probes. Intel iOS
+simulator frameworks are built, but executing Intel or physical-device tests
+requires suitable hardware and runtimes outside these hosted jobs.
+Shared Kotlin changes also trigger the existing Android and iOS test paths. This source directory and its
+wrapper are included in the npm package; generated build outputs and local Gradle
+caches are not.
diff --git a/packages/react-native/ReactShared/React-KMP.podspec b/packages/react-native/ReactShared/React-KMP.podspec
new file mode 100644
index 000000000000..9a36d38ba47f
--- /dev/null
+++ b/packages/react-native/ReactShared/React-KMP.podspec
@@ -0,0 +1,36 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+require 'json'
+
+package = JSON.parse(File.read(File.join(__dir__, '..', 'package.json')))
+
+Pod::Spec.new do |s|
+  s.name = 'React-KMP'
+  s.version = package['version']
+  s.summary = 'Opt-in shared Kotlin algorithms for React Native.'
+  s.homepage = 'https://reactnative.dev/'
+  s.license = package['license']
+  s.author = 'Meta Platforms, Inc. and its affiliates'
+  s.source = { :git => 'https://github.com/facebook/react-native.git', :tag => "v#{package['version']}" }
+  s.platforms = min_supported_versions
+  # The small support target establishes build ordering without trying to link an
+  # iOS-only vendored XCFramework when the application is built for Catalyst.
+  s.source_files = 'cocoapods/ReactNativeShared.m'
+  s.preserve_paths = 'src/**/*', 'gradle/**/*', 'gradlew', '*.kts', '*.properties', 'scripts/**/*'
+  s.pod_target_xcconfig = { 'ENABLE_USER_SCRIPT_SANDBOXING' => 'NO' }
+  s.user_target_xcconfig = {
+    'FRAMEWORK_SEARCH_PATHS[sdk=iphoneos*]' => '$(inherited) "$(PODS_CONFIGURATION_BUILD_DIR)/ReactNativeSharedKMP"',
+    'FRAMEWORK_SEARCH_PATHS[sdk=iphonesimulator*]' => '$(inherited) "$(PODS_CONFIGURATION_BUILD_DIR)/ReactNativeSharedKMP"',
+  }
+  # Link flags are added to direct consumers in react_native_post_install.
+  # user_target_xcconfig also reaches tests that inherit only search paths.
+  s.script_phase = {
+    :name => 'Build shared Kotlin framework',
+    :execution_position => :before_compile,
+    :always_out_of_date => '1',
+    :script => '"${PODS_TARGET_SRCROOT}/scripts/build-apple-framework.sh"',
+  }
+end
diff --git a/packages/react-native/ReactShared/build.gradle.kts b/packages/react-native/ReactShared/build.gradle.kts
new file mode 100644
index 000000000000..a383ea7ec72a
--- /dev/null
+++ b/packages/react-native/ReactShared/build.gradle.kts
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import java.util.Properties
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinNativeTarget
+
+plugins { kotlin("multiplatform") version "2.4.20" }
+
+group = "com.facebook.react"
+
+val reactAndroidProperties = Properties()
+
+file("../ReactAndroid/gradle.properties").inputStream().use(reactAndroidProperties::load)
+
+version = reactAndroidProperties.getProperty("VERSION_NAME")
+
+val smokeEnabled =
+    providers.gradleProperty("reactNativeSharedSmoke").map { it.toBooleanStrict() }.getOrElse(false)
+
+if (smokeEnabled) {
+  // Keep test-only exports separate from any future production artifacts.
+  layout.buildDirectory.set(layout.projectDirectory.dir("build/smoke"))
+}
+
+kotlin {
+  explicitApi()
+  jvmToolchain(17)
+  compilerOptions {
+    // ReactAndroid consumers still compile with the older Kotlin language level.
+    languageVersion.set(KotlinVersion.KOTLIN_2_2)
+    apiVersion.set(KotlinVersion.KOTLIN_2_2)
+  }
+  jvm { compilerOptions { jvmTarget.set(JvmTarget.JVM_17) } }
+  iosArm64()
+  iosSimulatorArm64()
+  iosX64()
+
+  targets.withType<KotlinNativeTarget>().configureEach {
+    binaries.framework {
+      baseName = "ReactNativeShared"
+      isStatic = true
+      binaryOption("bundleId", "com.facebook.react.shared")
+    }
+  }
+
+  sourceSets {
+    commonMain.dependencies {
+      // Keep the JVM runtime dependency compatible with the existing Android library.
+      implementation(kotlin("stdlib", "2.2.0"))
+    }
+    commonTest.dependencies { implementation(kotlin("test")) }
+    if (smokeEnabled) {
+      commonMain { kotlin.srcDir("tests/smoke/kotlin") }
+      commonTest { kotlin.srcDir("tests/smoke/kotlinTest") }
+    }
+  }
+}
+
+// ReactAndroid embeds this JAR in its AAR, preserving the existing Maven coordinates.
+// A stable output path also works when this build is included by a source-build consumer.
+val jvmJar = tasks.named<Jar>("jvmJar")
+
+tasks.register<Sync>("exportAndroidJar") {
+  from(jvmJar.flatMap { it.archiveFile })
+  into(layout.buildDirectory.dir("android"))
+  rename { "react-native-shared.jar" }
+}
diff --git a/packages/react-native/ReactShared/cocoapods/ReactNativeShared.m b/packages/react-native/ReactShared/cocoapods/ReactNativeShared.m
new file mode 100644
index 000000000000..5dc776e831f0
--- /dev/null
+++ b/packages/react-native/ReactShared/cocoapods/ReactNativeShared.m
@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// The support pod orders the Kotlin framework build before React-RCTFabric.
+// All shared implementations are supplied by ReactNativeShared.framework.
diff --git a/packages/react-native/ReactShared/gradle.properties b/packages/react-native/ReactShared/gradle.properties
new file mode 100644
index 000000000000..e8b989142732
--- /dev/null
+++ b/packages/react-native/ReactShared/gradle.properties
@@ -0,0 +1,3 @@
+org.gradle.jvmargs=-Xmx2g -XX:MaxMetaspaceSize=768m -Dfile.encoding=UTF-8
+org.gradle.caching=true
+kotlin.stdlib.default.dependency=false
diff --git a/packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.jar b/packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 000000000000..d997cfc60f4c
Binary files /dev/null and b/packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.properties b/packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 000000000000..80d82296e83e
--- /dev/null
+++ b/packages/react-native/ReactShared/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,8 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.4.1-bin.zip
+distributionSha256Sum=2ab2958f2a1e51120c326cad6f385153bb11ee93b3c216c5fccebfdfbb7ec6cb
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/packages/react-native/ReactShared/gradlew b/packages/react-native/ReactShared/gradlew
new file mode 100755
index 000000000000..739907dfd159
--- /dev/null
+++ b/packages/react-native/ReactShared/gradlew
@@ -0,0 +1,248 @@
+#!/bin/sh
+
+#
+# Copyright © 2015 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/2d6327017519d23b96af35865dc997fcb544fb40/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s\n' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/packages/react-native/ReactShared/gradlew.bat b/packages/react-native/ReactShared/gradlew.bat
new file mode 100644
index 000000000000..c4bdd3ab8e3c
--- /dev/null
+++ b/packages/react-native/ReactShared/gradlew.bat
@@ -0,0 +1,93 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -jar "%APP_HOME%\gradle\wrapper\gradle-wrapper.jar" %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/packages/react-native/ReactShared/scripts/benchmark-apple-gradient.py b/packages/react-native/ReactShared/scripts/benchmark-apple-gradient.py
new file mode 100644
index 000000000000..8566c4557c47
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/benchmark-apple-gradient.py
@@ -0,0 +1,145 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""Measure the real native and KMP adapters in separate Release executables.
+
+Requires the same toolchain and simulator runtime as test-apple-gradient.sh.
+Results are simulator microbenchmarks, not device or application benchmarks.
+"""
+
+import argparse
+import hashlib
+import json
+import os
+import pathlib
+import platform
+import statistics
+import subprocess
+import time
+
+
+def run(command, **kwargs):
+    started = time.perf_counter()
+    result = subprocess.run(command, capture_output=True, text=True, **kwargs)
+    if result.returncode:
+        raise RuntimeError(
+            f"Command failed ({result.returncode}): {command}\n"
+            + (result.stdout + result.stderr)[-12000:]
+        )
+    return result, time.perf_counter() - started
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--build-only", action="store_true", help="Compile without accessing the simulator.")
+    parser.add_argument("--iterations", type=int, default=2000)
+    parser.add_argument("--samples", type=int, default=7)
+    parser.add_argument("--repeats", type=int, default=3, help="Fresh processes per case and variant.")
+    parser.add_argument("--output", type=pathlib.Path)
+    parser.add_argument("--prepared-release-dir", type=pathlib.Path,
+                        help="Reuse artifacts previously built by test-apple-gradient.sh with RCT_KMP_BUILD_TYPE=Release.")
+    args = parser.parse_args()
+    if not 1 <= args.iterations <= 1000000 or not 1 <= args.samples <= 100 or not 1 <= args.repeats <= 100:
+        parser.error("iterations must be 1..1000000; samples and repeats must be 1..100")
+    shared = pathlib.Path(__file__).resolve().parent.parent
+    react = shared.parent
+    output = (args.output or shared / "build/apple-gradient-benchmark").resolve()
+    output.mkdir(parents=True, exist_ok=True)
+    prepared = args.prepared_release_dir.resolve() if args.prepared_release_dir else output / "prepared"
+    preparation_seconds = None
+    if not args.prepared_release_dir:
+        env = dict(os.environ, RCT_KMP_BUILD_TYPE="Release", RCT_KMP_BUILD_ONLY="1", RCT_KMP_TEST_OUTPUT_DIR=str(prepared))
+        preparation, preparation_seconds = run([str(shared / "scripts/test-apple-gradient.sh")], env=env)
+        (output / "prepare.log").write_text(preparation.stdout + preparation.stderr)
+    sdk = run(["xcrun", "--sdk", "iphonesimulator", "--show-sdk-path"])[0].stdout.strip()
+    architecture = platform.machine()
+    graphics = react / "ReactCommon/react/renderer/graphics"
+    flags = [
+        "-std=c++20", "-O2", "-fobjc-arc", "-DREACT_NATIVE_PRODUCTION", "-DRCTLOG_ENABLED=0",
+        "-include", "memory", "-include", "vector", "-target", f"{architecture}-apple-ios15.1-simulator",
+        "-isysroot", sdk, "-I", str(prepared / "include"), "-I", str(react / "ReactCommon"),
+        "-I", str(graphics / "platform/ios"), "-F", str(prepared / "ReactNativeSharedKMP"),
+    ]
+    native_objects = [str(prepared / name) for name in [
+        "RCTAnimationUtils.mm.o", "Color.cpp.o", "ColorComponents.cpp.o", "HostPlatformColor.mm.o",
+        "RCTPlatformColorUtils.mm.o", "ManagedObjectWrapper.mm.o",
+    ]]
+    frameworks = ["-framework", "Foundation", "-framework", "UIKit", "-framework", "QuartzCore", "-framework", "CoreGraphics"]
+    builds = {}
+    executables = {}
+    for variant in ("native", "kmp"):
+        adapter = output / f"{variant}-adapter.o"
+        defines = ["-DRCT_USE_KMP=1"] if variant == "kmp" else ["-DRCT_USE_KMP=0", "-DRCTGradientUtils=RCTGradientUtilsBaseline"]
+        _, compile_seconds = run(["xcrun", "clang++", *flags, *defines, "-c", str(react / "React/Fabric/Utils/RCTGradientUtils.mm"), "-o", str(adapter)])
+        executable = output / f"AppleGradientBenchmark-{variant}"
+        link = ["xcrun", "clang++", *flags, f"-DRCT_BENCHMARK_KMP={int(variant == 'kmp')}",
+                str(shared / "tests/AppleGradientBenchmark.mm"), str(adapter), *native_objects,
+                *frameworks, "-Wl,-dead_strip", "-o", str(executable)]
+        if variant == "kmp":
+            link.extend(["-framework", "ReactNativeShared"])
+        _, link_seconds = run(link)
+        executables[variant] = executable
+        builds[variant] = {"adapterCompileSeconds": compile_seconds, "harnessCompileAndLinkSeconds": link_seconds,
+                           "executableBytes": executable.stat().st_size}
+        size = run(["xcrun", "size", "-m", str(executable)])[0].stdout
+        (output / f"{variant}-segments.txt").write_text(size)
+    framework = prepared / "ReactNativeSharedKMP/ReactNativeShared.framework/ReactNativeShared"
+    report = {
+        "configuration": "Release; clang -O2; dead stripping; separate native-only and KMP executables",
+        "platform": "iOS simulator", "hostArchitecture": architecture, "sdk": sdk,
+        "xcode": run(["xcodebuild", "-version"])[0].stdout.strip(),
+        "preparationSeconds": preparation_seconds, "builds": builds,
+        "reusedReleaseArtifacts": bool(args.prepared_release_dir),
+        "artifactSha256": {str(path): hashlib.sha256(path.read_bytes()).hexdigest()
+                           for path in [framework, *(pathlib.Path(item) for item in native_objects)]},
+        "staticFrameworkBytes": framework.stat().st_size,
+        "incrementalExecutableBytes": builds["kmp"]["executableBytes"] - builds["native"]["executableBytes"],
+        "runtimeExecuted": False, "measurements": [], "firstCallProcesses": [],
+        "limitations": [
+            "Simulator results are not physical-device performance or RN application startup.",
+            "First-call latency starts after inputs exist; process elapsed time includes simctl/OS launch overhead.",
+            "Memory values are process footprint snapshots, not total allocated bytes; Kotlin GC is not forced.",
+            "Binary size is this isolated executable, not an installed, signed, or compressed application delta.",
+            "Compilation timings are one warm-cache observation; preparation includes framework and parity harness builds.",
+        ],
+    }
+    if not args.build_only:
+        simulator = os.environ.get("RCT_KMP_SIMULATOR_UDID")
+        if not simulator:
+            devices = json.loads(run(["xcrun", "simctl", "list", "devices", "available", "-j"])[0].stdout)["devices"]
+            simulator = next((items[0]["udid"] for runtime, items in devices.items() if ".iOS-" in runtime and items), None)
+        if not simulator:
+            raise RuntimeError("Install a compatible iOS simulator runtime or set RCT_KMP_SIMULATOR_UDID.")
+        for repetition in range(args.repeats):
+            for variant in (("native", "kmp") if repetition % 2 == 0 else ("kmp", "native")):
+                result, elapsed = run(["xcrun", "simctl", "spawn", "--standalone", simulator,
+                                       str(executables[variant]), "two_stops", "1", "1", "--first-call-only"])
+                measurement = json.loads(result.stdout)
+                measurement.update(repetition=repetition, processElapsedSeconds=elapsed)
+                report["firstCallProcesses"].append(measurement)
+                (output / f"first-call-{variant}-{repetition}.stderr.log").write_text(result.stderr)
+        cases = ("two_stops", "implicit_16", "explicit_64", "asymmetric_hint", "multiple_hints")
+        for repetition in range(args.repeats):
+            for case in cases:
+                # Alternate order across independent processes to reduce ordering bias.
+                for variant in (("native", "kmp") if repetition % 2 == 0 else ("kmp", "native")):
+                    result, elapsed = run(["xcrun", "simctl", "spawn", "--standalone", simulator,
+                                           str(executables[variant]), case, str(args.iterations), str(args.samples)])
+                    measurement = json.loads(result.stdout)
+                    measurement.update(repetition=repetition, processElapsedSeconds=elapsed)
+                    measurement["medianNanosecondsPerCall"] = statistics.median(measurement["nanosecondsPerCall"])
+                    report["measurements"].append(measurement)
+                    (output / f"{case}-{variant}-{repetition}.stderr.log").write_text(result.stderr)
+                pair = report["measurements"][-2:]
+                if pair[0]["checksum"] != pair[1]["checksum"]:
+                    raise RuntimeError(f"Observed output checksum differs for {case}; inspect parity before comparing timings.")
+        report["runtimeExecuted"] = True
+    (output / "results.json").write_text(json.dumps(report, indent=2) + "\n")
+    print(f"{'Compiled' if args.build_only else 'Measured'} native and KMP gradient executables: {output / 'results.json'}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/packages/react-native/ReactShared/scripts/benchmark-kmp-build.py b/packages/react-native/ReactShared/scripts/benchmark-kmp-build.py
new file mode 100644
index 000000000000..f748e0bfded3
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/benchmark-kmp-build.py
@@ -0,0 +1,81 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""Measure clean, unchanged, and edited shared-module builds in an isolated copy.
+
+Dependency/compiler caches stay warm. Gradle's build-output cache is disabled so
+the clean build measures compilation instead of restoring another build's outputs.
+This measures the added shared module, not the entire Android or iOS application.
+"""
+
+import argparse
+import json
+import pathlib
+import platform
+import shutil
+import subprocess
+import time
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--plan-only", action="store_true", help="Print the measurement plan without building.")
+    parser.add_argument("--output", type=pathlib.Path)
+    args = parser.parse_args()
+    shared = pathlib.Path(__file__).resolve().parent.parent
+    output = (args.output or shared / "build/kmp-build-benchmark").resolve()
+    output.mkdir(parents=True, exist_ok=True)
+    target = "IosSimulatorArm64" if platform.machine() == "arm64" else "IosX64"
+    tasks = ["jvmTest", f"linkReleaseFramework{target}"]
+    phases = [
+        {"name": "clean_outputs", "tasks": ["clean", *tasks]},
+        {"name": "unchanged_incremental", "tasks": tasks},
+        {"name": "edited_common_source", "tasks": tasks},
+    ]
+    report = {
+        "dependencyAndCompilerCaches": "warm; existing user caches",
+        "gradleBuildOutputCache": "disabled", "measurementsExecuted": False,
+        "scope": "isolated shared module; not total application build time",
+        "sourceEdit": "append a comment to the copied common source; original source remains unchanged",
+        "phases": phases,
+    }
+    if not args.plan_only:
+        if platform.system() != "Darwin":
+            parser.error("The paired JVM/iOS measurement requires macOS and Xcode.")
+        fixture = output / "fixture"
+        if fixture.exists():
+            parser.error(f"Choose a fresh --output directory; fixture already exists: {fixture}")
+        copied_shared = fixture / "ReactShared"
+        copied_shared.mkdir(parents=True)
+        for name in ("build.gradle.kts", "settings.gradle.kts", "gradle.properties", "gradlew", "gradlew.bat", "gradle", "src"):
+            source = shared / name
+            if source.is_dir():
+                shutil.copytree(source, copied_shared / name)
+            else:
+                shutil.copy2(source, copied_shared / name)
+        (fixture / "ReactAndroid").mkdir()
+        shutil.copy2(shared.parent / "ReactAndroid/gradle.properties", fixture / "ReactAndroid/gradle.properties")
+        for phase in phases:
+            if phase["name"] == "edited_common_source":
+                source = copied_shared / "src/commonMain/kotlin/com/facebook/react/shared/GradientStops.kt"
+                with source.open("a") as stream:
+                    stream.write("\n// Non-semantic edit in the isolated build-cost fixture.\n")
+            command = [str(copied_shared / "gradlew"), *phase["tasks"], "--no-build-cache", "--max-workers=2", "--console=plain"]
+            started = time.perf_counter()
+            completed = subprocess.run(command, cwd=copied_shared, capture_output=True, text=True)
+            phase.update(elapsedSeconds=time.perf_counter() - started, exitCode=completed.returncode)
+            (output / f"{phase['name']}.log").write_text(completed.stdout + completed.stderr)
+            if completed.returncode != 0:
+                report["failurePhase"] = phase["name"]
+                (output / "results.json").write_text(json.dumps(report, indent=2) + "\n")
+                raise SystemExit(f"Build measurement failed in {phase['name']}; inspect {output}.")
+        report["measurementsExecuted"] = True
+    (output / "results.json").write_text(json.dumps(report, indent=2) + "\n")
+    print(f"{'Planned' if args.plan_only else 'Measured'} shared-module build costs: {output / 'results.json'}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/packages/react-native/ReactShared/scripts/build-apple-framework.sh b/packages/react-native/ReactShared/scripts/build-apple-framework.sh
new file mode 100755
index 000000000000..16a5becb27c0
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/build-apple-framework.sh
@@ -0,0 +1,52 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -euo pipefail
+
+if [[ "${EFFECTIVE_PLATFORM_NAME:-}" == "-maccatalyst" || "${IS_MACCATALYST:-NO}" == "YES" ]]; then
+  echo 'React Native KMP: Catalyst uses the existing native gradient implementation.'
+  exit 0
+fi
+
+if [[ "${ACTION:-}" == "clean" ]]; then
+  exit 0
+fi
+
+shared_root="$(cd "$(dirname "$0")/.." && pwd)"
+build_type="${RCT_KMP_BUILD_TYPE:-${CONFIGURATION:-Debug}}"
+case "$build_type" in
+  Debug|*Debug*) build_type=Debug; framework_variant=debugFramework ;;
+  Release|*Release*) build_type=Release; framework_variant=releaseFramework ;;
+  *) echo 'error: Set RCT_KMP_BUILD_TYPE=Debug or Release for a custom Xcode configuration.' >&2; exit 1 ;;
+esac
+
+read -r -a architectures <<< "${ARCHS:-arm64}"
+gradle_tasks=()
+frameworks=()
+for architecture in "${architectures[@]}"; do
+  case "${PLATFORM_NAME:-}:$architecture" in
+    iphoneos:arm64) kotlin_target=iosArm64; task_target=IosArm64 ;;
+    iphonesimulator:arm64) kotlin_target=iosSimulatorArm64; task_target=IosSimulatorArm64 ;;
+    iphonesimulator:x86_64) kotlin_target=iosX64; task_target=IosX64 ;;
+    *) echo "error: React Native KMP has no framework for ${PLATFORM_NAME:-unknown}:$architecture." >&2; exit 1 ;;
+  esac
+  gradle_tasks+=("link${build_type}Framework${task_target}")
+  frameworks+=("$shared_root/build/bin/$kotlin_target/$framework_variant/ReactNativeShared.framework")
+done
+
+"$shared_root/gradlew" -p "$shared_root" --console=plain "${gradle_tasks[@]}"
+
+destination="${PODS_CONFIGURATION_BUILD_DIR:?Run this script from the React-KMP CocoaPods build phase}/ReactNativeSharedKMP"
+mkdir -p "$destination"
+rm -rf "$destination/ReactNativeShared.framework"
+ditto "${frameworks[0]}" "$destination/ReactNativeShared.framework"
+if [[ ${#frameworks[@]} -gt 1 ]]; then
+  binaries=()
+  for framework in "${frameworks[@]}"; do
+    binaries+=("$framework/ReactNativeShared")
+  done
+  xcrun lipo -create "${binaries[@]}" -output "$destination/ReactNativeShared.framework/ReactNativeShared"
+fi
diff --git a/packages/react-native/ReactShared/scripts/test-android-consumers.py b/packages/react-native/ReactShared/scripts/test-android-consumers.py
new file mode 100644
index 000000000000..431df5a5da09
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-android-consumers.py
@@ -0,0 +1,474 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""Build fresh Android consumers of the Maven AAR and packed npm source.
+
+Requires Python 3.12+, Node/Yarn/npm, JDK 17 and the Android SDK/NDK. Run after
+the repository's Yarn install. A supplied device runs both release APKs; without
+one the report explicitly records compilation/packaging validation only.
+The packed-source build also builds Hermes from source, as the standard React
+Native composite does; the repository-only stable-Hermes flag does not apply.
+"""
+
+import argparse
+from collections import Counter
+import hashlib
+import io
+import json
+import os
+from pathlib import Path
+import re
+import shutil
+import subprocess
+import tarfile
+import tempfile
+import textwrap
+import time
+import tomllib
+import uuid
+import zipfile
+
+
+SHARED = Path(__file__).resolve().parents[1]
+RN = SHARED.parent
+REPOSITORY = RN.parent.parent
+
+
+def write(path, content):
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(textwrap.dedent(content).lstrip(), encoding="utf-8")
+
+
+def groovy_string(value):
+    return "'" + str(value).replace("\\", "\\\\").replace("'", "\\'") + "'"
+
+
+def run(command, cwd, log, env=None):
+    print("Running: " + " ".join(map(str, command)), flush=True)
+    with log.open("w", encoding="utf-8") as output:
+        subprocess.run(command, cwd=cwd, env=env, stdout=output,
+                       stderr=subprocess.STDOUT, check=True)
+
+
+def properties(path):
+    return dict(line.strip().split("=", 1) for line in path.read_text().splitlines()
+                if "=" in line and not line.lstrip().startswith("#"))
+
+
+def pack(package, destination, environment):
+    result = subprocess.run(
+        ["npm", "pack", "--ignore-scripts", "--json", "--pack-destination", str(destination)],
+        cwd=package, env=environment, check=True, capture_output=True, text=True,
+    )
+    metadata = json.loads(result.stdout)
+    if isinstance(metadata, dict):
+        metadata = [metadata] if "filename" in metadata else list(metadata.values())
+    if len(metadata) != 1:
+        raise AssertionError(f"Expected one npm package: {metadata}")
+    return destination / metadata[0]["filename"]
+
+
+def unpack(archive, destination):
+    destination.mkdir(parents=True, exist_ok=True)
+    with tarfile.open(archive) as tar:
+        members = tar.getmembers()
+        if any(not member.name.startswith("package/") for member in members):
+            raise AssertionError(f"Unexpected npm archive layout: {archive}")
+        for member in members:
+            member.name = member.name.removeprefix("package/")
+        tar.extractall(destination, members=members, filter="data")
+
+
+def inspect_aar(aar):
+    classes = Counter()
+    with zipfile.ZipFile(aar) as archive:
+        for entry in archive.namelist():
+            if entry == "classes.jar" or (entry.startswith("libs/") and entry.endswith(".jar")):
+                with zipfile.ZipFile(io.BytesIO(archive.read(entry))) as jar:
+                    classes.update(name for name in jar.namelist()
+                                   if name.startswith("com/facebook/react/shared/")
+                                   and name.endswith(".class"))
+    required = {f"com/facebook/react/shared/{name}.class"
+                for name in ["GradientStops", "GradientStopInput", "ResolvedGradientStop",
+                             "MultipartFraming", "MultipartChunk", "MultipartHeaders", "MultipartHeader",
+                             "ScrollSnapOffsets", "ScrollSnapDirection", "ScrollSnapResult"]}
+    if not required.issubset(classes) or any(count != 1 for count in classes.values()):
+        raise AssertionError(f"Missing or duplicated shared classes in {aar}: {classes}")
+    with tempfile.TemporaryDirectory(prefix="react-native-kmp-bytecode-") as directory:
+        jar = Path(directory) / "classes.jar"
+        with zipfile.ZipFile(aar) as archive:
+            jar.write_bytes(archive.read("classes.jar"))
+        adapters = {
+            "com.facebook.react.uimanager.style.ColorStopUtils": ("GradientStops.resolve",),
+            "com.facebook.react.devsupport.MultipartStreamReader": (
+                "MultipartFraming.nextChunk", "MultipartHeaders.parse"),
+        }
+        for view in ("ReactScrollView", "ReactHorizontalScrollView", "ReactNestedScrollView"):
+            adapters[f"com.facebook.react.views.scroll.{view}"] = ("ScrollSnapOffsets.resolve",)
+        for adapter, methods in adapters.items():
+            bytecode = subprocess.check_output(
+                ["javap", "-c", "-p", "-classpath", str(jar), adapter], text=True)
+            for method in methods:
+                pattern = r"invoke(?:static|virtual)\s+.*// Method com/facebook/react/shared/" + re.escape(method) + r"(?:\$default)?:"
+                if not re.search(pattern, bytecode):
+                    raise AssertionError(f"{adapter} does not invoke shared {method} in {aar}")
+    return {"path": str(aar), "sha256": hashlib.sha256(aar.read_bytes()).hexdigest(),
+            "shared_class_counts": dict(classes), "adapter_invokes_shared_resolver": True}
+
+
+ACTIVITY = r"""
+package com.facebook.react.kmp.consumer;
+
+import android.app.Activity;
+import android.graphics.Color;
+import android.os.Bundle;
+import android.util.DisplayMetrics;
+import android.util.Log;
+import android.widget.TextView;
+import com.facebook.react.devsupport.MultipartStreamReader;
+import com.facebook.react.uimanager.DisplayMetricsHolder;
+import com.facebook.react.uimanager.LengthPercentage;
+import com.facebook.react.uimanager.LengthPercentageType;
+import com.facebook.react.uimanager.style.ColorStop;
+import com.facebook.react.uimanager.style.ColorStopUtils;
+import com.facebook.react.uimanager.style.ProcessedColorStop;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.io.IOException;
+import okio.Buffer;
+import okio.BufferedSource;
+
+// Java deliberately exercises the packaged Android adapter through its JVM API.
+// No shared source files or replacement implementation are compiled into this app.
+public final class MainActivity extends Activity {
+  @Override public void onCreate(Bundle state) {
+    super.onCreate(state);
+    DisplayMetrics metrics = new DisplayMetrics();
+    metrics.setTo(getResources().getDisplayMetrics());
+    metrics.density = 2f;
+    DisplayMetricsHolder.setScreenDisplayMetrics(metrics);
+    List<ProcessedColorStop> density = ColorStopUtils.INSTANCE.getFixedColorStops(
+        Arrays.asList(new ColorStop(Color.RED,
+            new LengthPercentage(25f, LengthPercentageType.POINT)),
+            new ColorStop(Color.BLUE, null)), 200f);
+    if (density.get(0).getPosition() != .25f) throw new AssertionError("Android density");
+    List<ProcessedColorStop> hint = ColorStopUtils.INSTANCE.getFixedColorStops(
+        Arrays.asList(new ColorStop(Color.argb(128, 255, 0, 0), null),
+            new ColorStop(null, new LengthPercentage(25f, LengthPercentageType.PERCENT)),
+            new ColorStop(Color.BLUE, null)), 100f);
+    if (hint.size() != 11 || hint.get(3).getPosition() != .25f
+        || hint.get(3).getColor() != Color.argb(191, 127, 0, 127)) {
+      throw new AssertionError("Shared hint expansion or Android alpha rounding");
+    }
+    checkMultipart();
+    String result = "KMP consumer PASS " + BuildConfig.CONSUMER_MODE
+        + " " + getIntent().getStringExtra("validationToken");
+    TextView text = new TextView(this);
+    text.setText(result);
+    setContentView(text);
+    Log.i("KmpConsumer", result);
+  }
+
+  private static void checkMultipart() {
+    // The first body ends in CRLF, so a header marker can straddle the boundary.
+    Buffer input = new Buffer().writeUtf8(
+        "\r\n--sample\r\nfirst\r\n\r\n--sample\r\n"
+        + "content-type: text/plain\r\n\r\nsecond\r\n--sample--\r\n");
+    int[] parts = {0};
+    try {
+      boolean complete = new MultipartStreamReader(input, "sample").readAllParts(
+          new MultipartStreamReader.ChunkListener() {
+            @Override public void onChunkComplete(
+                Map<String, String> headers, BufferedSource body, boolean last) throws IOException {
+              int index = parts[0]++;
+              String expected = index == 0 ? "first\r\n" : "second";
+              if (index > 1 || !expected.equals(body.readUtf8()) || last != (index == 1)) {
+                throw new AssertionError("Shared multipart body or completion");
+              }
+              if (index == 0 ? !headers.isEmpty()
+                  : !"text/plain".equals(headers.get("CONTENT-TYPE"))) {
+                throw new AssertionError("Android multipart header policy");
+              }
+            }
+            @Override public void onChunkProgress(
+                Map<String, String> headers, long loaded, long total) {}
+          });
+      if (!complete || parts[0] != 2) throw new AssertionError("Shared multipart framing");
+    } catch (IOException error) {
+      throw new AssertionError(error);
+    }
+  }
+}
+"""
+
+
+def fixture(path, mode, versions, version, hermes_version, maven, abi):
+    source_builds = """
+        includeBuild('node_modules/@react-native/gradle-plugin')
+        includeBuild('node_modules/react-native') {
+          name = 'react-native-build-from-source'
+          dependencySubstitution {
+            substitute module('com.facebook.react:react-android') using project(':packages:react-native:ReactAndroid')
+            substitute module('com.facebook.hermes:hermes-android') using project(':packages:react-native:ReactAndroid:hermes-engine')
+          }
+        }
+    """ if mode == "source" else ""
+    write(path / "settings.gradle", f"""
+        pluginManagement {{ repositories {{ google(); mavenCentral(); gradlePluginPortal() }} }}
+        dependencyResolutionManagement {{
+          repositories {{
+            exclusiveContent {{
+              forRepository {{ maven {{ url = uri({groovy_string(maven)}) }} }}
+              filter {{ includeModule('com.facebook.react', 'react-android') }}
+            }}
+            google()
+            mavenCentral()
+          }}
+        }}
+        rootProject.name = 'kmp-{mode}-consumer'
+        include ':app'
+        {source_builds}
+    """)
+    write(path / "gradle.properties", """
+        android.useAndroidX=true
+        org.gradle.jvmargs=-Xmx4g -XX:MaxMetaspaceSize=1g
+        org.gradle.caching=true
+    """)
+    if mode == "source":
+        write(path / "build.gradle", """
+            tasks.register('prepareSourceAars') {
+              dependsOn gradle.includedBuild('react-native-build-from-source').task(':packages:react-native:ReactAndroid:bundleDebugAar')
+              dependsOn gradle.includedBuild('react-native-build-from-source').task(':packages:react-native:ReactAndroid:bundleReleaseAar')
+            }
+        """)
+    write(path / "app/build.gradle", f"""
+        import groovy.json.JsonOutput
+        import org.gradle.api.artifacts.component.ModuleComponentIdentifier
+        import org.gradle.api.artifacts.component.ProjectComponentIdentifier
+
+        plugins {{ id 'com.android.application' version '{versions['agp']}' }}
+        android {{
+          namespace 'com.facebook.react.kmp.consumer'
+          compileSdk {versions['compileSdk']}
+          ndkVersion '{versions['ndkVersion']}'
+          defaultConfig {{
+            applicationId 'com.facebook.react.kmp.consumer.{mode}'
+            minSdk {versions['minSdk']}
+            targetSdk {versions['targetSdk']}
+            versionCode 1
+            versionName '1.0'
+            ndk {{ abiFilters '{abi}' }}
+            buildConfigField 'String', 'CONSUMER_MODE', '"{mode}"'
+          }}
+          buildFeatures {{ buildConfig true }}
+          // Match React Native's Gradle plugin rules for shared Prefab libraries.
+          packaging {{
+            jniLibs.pickFirsts += ['**/libfbjni.so', '**/libreactnative.so', '**/libjsi.so',
+                                  '**/libc++_shared.so', '**/libhermesvm.so', '**/libhermestooling.so']
+          }}
+          compileOptions {{
+            sourceCompatibility JavaVersion.VERSION_17
+            targetCompatibility JavaVersion.VERSION_17
+          }}
+          buildTypes {{
+            release {{
+              minifyEnabled true
+              shrinkResources true
+              signingConfig signingConfigs.debug
+              proguardFiles getDefaultProguardFile('proguard-android-optimize.txt')
+            }}
+          }}
+        }}
+        dependencies {{
+          implementation 'com.facebook.react:react-android:{version}'
+          implementation 'com.facebook.hermes:hermes-android:{hermes_version}'
+        }}
+        tasks.register('verifyResolution') {{
+          dependsOn 'assembleDebug', 'assembleRelease'
+          {"dependsOn ':prepareSourceAars'" if mode == "source" else ""}
+          doLast {{
+            def result = ['debug', 'release'].collectEntries {{ variant ->
+              def configuration = configurations.getByName(variant + 'RuntimeClasspath')
+              def components = configuration.incoming.resolutionResult.allComponents.findAll {{ component ->
+                def id = component.id
+                (id instanceof ModuleComponentIdentifier && id.group == 'com.facebook.react' && id.module == 'react-android') ||
+                    (id instanceof ProjectComponentIdentifier && id.projectPath.endsWith(':ReactAndroid'))
+              }}
+              assert components.size() == 1 : components
+              def id = components.first().id
+              assert {str(mode == 'source').lower()} == (id instanceof ProjectComponentIdentifier) : id
+              if (id instanceof ModuleComponentIdentifier) assert id.version == '{version}' : id
+              def artifacts = configuration.incoming.artifactView {{
+                componentFilter {{ component -> component == id }}
+                {"attributes.attribute(org.gradle.api.artifacts.type.ArtifactTypeDefinition.ARTIFACT_TYPE_ATTRIBUTE, 'android-classes-jar')" if mode == "source" else ""}
+              }}.artifacts.artifacts
+              assert !artifacts.empty
+              def engines = configuration.incoming.resolutionResult.allComponents.findAll {{ component ->
+                def engine = component.id
+                (engine instanceof ModuleComponentIdentifier && engine.group == 'com.facebook.hermes' && engine.module == 'hermes-android') ||
+                    (engine instanceof ProjectComponentIdentifier && engine.projectPath.endsWith(':hermes-engine'))
+              }}
+              assert engines.size() == 1 : engines
+              def engine = engines.first().id
+              assert {str(mode == 'source').lower()} == (engine instanceof ProjectComponentIdentifier) : engine
+              if (engine instanceof ModuleComponentIdentifier) assert engine.version == '{hermes_version}' : engine
+              [(variant): [component: id.displayName, artifacts: artifacts.collect {{ it.file.absolutePath }}, hermes_component: engine.displayName]]
+            }}
+            file(layout.buildDirectory.file('consumer-resolution.json')).text = JsonOutput.prettyPrint(JsonOutput.toJson(result))
+          }}
+        }}
+    """)
+    write(path / "app/src/main/AndroidManifest.xml", """
+        <manifest xmlns:android="http://schemas.android.com/apk/res/android">
+          <application android:label="KMP consumer" android:theme="@android:style/Theme.Material.Light.NoActionBar">
+            <activity android:name="com.facebook.react.kmp.consumer.MainActivity" android:exported="true">
+              <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+              </intent-filter>
+            </activity>
+          </application>
+        </manifest>
+    """)
+    write(path / "app/src/main/java/com/facebook/react/kmp/consumer/MainActivity.java", ACTIVITY)
+
+
+def device_check(adb, serial, fixture_dir, mode, log):
+    package = f"com.facebook.react.kmp.consumer.{mode}"
+    apk = fixture_dir / "app/build/outputs/apk/release/app-release.apk"
+    prefix = [adb, "-s", serial]
+    token = uuid.uuid4().hex
+    with log.open("w", encoding="utf-8") as output:
+        subprocess.run(prefix + ["install", "-r", str(apk)], stdout=output,
+                       stderr=subprocess.STDOUT, check=True)
+        try:
+            subprocess.run(prefix + ["shell", "am", "start", "-W", "-n",
+                           package + "/com.facebook.react.kmp.consumer.MainActivity",
+                           "--es", "validationToken", token],
+                           stdout=output, stderr=subprocess.STDOUT, check=True)
+            for _ in range(20):
+                text = subprocess.check_output(prefix + ["logcat", "-d", "-s", "KmpConsumer:I", "*:S"], text=True)
+                if f"KMP consumer PASS {mode} {token}" in text:
+                    output.write(text)
+                    return {"serial": serial, "release_adapter_assertions": "passed"}
+                time.sleep(0.5)
+            raise AssertionError(f"Release app did not report successful adapter checks: {mode}")
+        finally:
+            subprocess.run(prefix + ["shell", "am", "force-stop", package], check=False)
+            subprocess.run(prefix + ["uninstall", package], stdout=output,
+                           stderr=subprocess.STDOUT, check=False)
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--output-dir", type=Path)
+    parser.add_argument("--maven-repository", type=Path, help="Use an existing real ReactAndroid Maven publication instead of publishing locally")
+    parser.add_argument("--device", help="adb serial for executing both minified release APKs")
+    parser.add_argument("--abi", default="arm64-v8a")
+    parser.add_argument("--max-workers", type=int, default=4, help="Maximum concurrent Gradle workers")
+    parser.add_argument("--prepare-only", action="store_true", help="Pack and prepare fixtures; do not claim build or runtime validation")
+    args = parser.parse_args()
+    if args.max_workers < 1:
+        parser.error("--max-workers must be positive")
+    output = args.output_dir.resolve() if args.output_dir else Path(tempfile.mkdtemp(prefix="react-native-kmp-android-"))
+    output.mkdir(parents=True, exist_ok=True)
+    if any((output / name).exists() for name in ["binary", "source"]):
+        parser.error("Use a fresh output directory; existing consumer fixtures are never overwritten")
+    environment = dict(os.environ, npm_config_cache=str(output / "npm-cache"),
+                       npm_config_fetch_timeout="30000", npm_config_fetch_retries="2")
+    packages = output / "packages"
+    packages.mkdir()
+    run(["yarn", "--cwd", str(REPOSITORY / "packages/react-native-codegen"), "build"], REPOSITORY, output / "codegen.log", environment)
+    archives = {name: pack(path, packages, environment) for name, path in {
+        "react-native": RN, "@react-native/codegen": REPOSITORY / "packages/react-native-codegen",
+        "@react-native/gradle-plugin": REPOSITORY / "packages/gradle-plugin",
+    }.items()}
+    source = output / "source"
+    for name, archive in archives.items():
+        unpack(archive, source / "node_modules" / name)
+    packed_rn = source / "node_modules/react-native"
+    excluded_parts = {"build", ".build", ".gradle", ".kotlin", ".cxx", ".swiftpm", "__pycache__"}
+    leaked = [str(path.relative_to(packed_rn)) for path in (packed_rn / "ReactShared").rglob("*")
+              if any(part in excluded_parts for part in path.relative_to(packed_rn / "ReactShared").parts)
+              or path.suffix in {".pyc", ".o", ".a", ".so", ".dylib", ".class", ".framework", ".xcframework"}]
+    if leaked:
+        raise AssertionError(f"Generated ReactShared outputs leaked into the npm archive: {leaked}")
+    versions = tomllib.loads((packed_rn / "gradle/libs.versions.toml").read_text())["versions"]
+    version = properties(packed_rn / "ReactAndroid/gradle.properties")["VERSION_NAME"]
+    hermes = properties(packed_rn / "sdks/hermes-engine/version.properties")["HERMES_VERSION_NAME"]
+    maven = args.maven_repository.resolve() if args.maven_repository else output / "maven"
+    for mode in ["binary", "source"]:
+        fixture(output / mode, mode, versions, version, hermes, maven, args.abi)
+    report = {"status": "prepared", "archives": {name: {"path": str(path), "sha256": hashlib.sha256(path.read_bytes()).hexdigest()} for name, path in archives.items()},
+              "maven_repository": str(maven), "abi": args.abi,
+              "hermes_build": {"publication": "stable Maven dependency", "packed_source": "standard Hermes source build"},
+              "consumers": {}}
+    report_file = output / "results.json"
+    report_file.write_text(json.dumps(report, indent=2) + "\n")
+    if args.prepare_only:
+        print(f"Prepared fixtures only; no Android builds or device tests ran. Report: {report_file}")
+        return
+    gradle = [str(REPOSITORY / "gradlew"), f"--max-workers={args.max_workers}", "--console=plain",
+              f"-PreactNativeArchitectures={args.abi}",
+              "-Dorg.gradle.internal.http.connectionTimeout=30000", "-Dorg.gradle.internal.http.socketTimeout=30000"]
+    try:
+        if not args.maven_repository:
+            init = output / "publication.gradle"
+            write(init, f"""
+                gradle.projectsEvaluated {{
+                  rootProject.allprojects.each {{ project ->
+                    def publishing = project.extensions.findByType(org.gradle.api.publish.PublishingExtension)
+                    publishing?.repositories?.withType(org.gradle.api.artifacts.repositories.MavenArtifactRepository)?.each {{ repository ->
+                      if (repository.name == 'mavenTempLocal') repository.url = project.uri({groovy_string(maven)})
+                    }}
+                  }}
+                }}
+            """)
+            run(gradle + ["-Preact.internal.useHermesStable=true", "--init-script", str(init), ":packages:react-native:ReactAndroid:publishReleasePublicationToMavenTempLocalRepository"], REPOSITORY, output / "publication.log")
+        aars = list((maven / "com/facebook/react/react-android" / version).glob("*.aar"))
+        if not aars:
+            raise AssertionError("The Maven publication contains no ReactAndroid AARs")
+        report["published_aars"] = [inspect_aar(aar) for aar in aars]
+        # Install dependencies for the packed tools, without installing an unpublished
+        # React Native version or replacing the extracted React Native source package.
+        write(source / "package.json", json.dumps({"private": True, "dependencies": {
+            name: f"file:{archives[name]}" for name in ["@react-native/codegen", "@react-native/gradle-plugin"]}}, indent=2))
+        run(["npm", "install", "--ignore-scripts", "--no-audit", "--no-fund"], source, output / "source-dependencies.log", environment)
+        # npm may prune the manually extracted package because it is deliberately not
+        # installed from the registry. Re-extract the same immutable npm archive.
+        if (source / "node_modules/react-native").exists():
+            shutil.rmtree(source / "node_modules/react-native")
+        unpack(archives["react-native"], source / "node_modules/react-native")
+        for mode in ["binary", "source"]:
+            consumer = output / mode
+            run(gradle + [":app:verifyResolution"], consumer, output / f"{mode}-build.log")
+            resolution = json.loads((consumer / "app/build/consumer-resolution.json").read_text())
+            report["consumers"][mode] = {"debug_and_minified_release": "passed", "resolution": resolution,
+                                          "runtime": "not run: no --device supplied"}
+            if mode == "source":
+                built = list((packed_rn / "ReactAndroid/build/outputs/aar").glob("*.aar"))
+                if not built:
+                    raise AssertionError("Packed-source consumer did not build a ReactAndroid AAR")
+                report["source_aars"] = [inspect_aar(aar) for aar in built]
+            if args.device:
+                sdk = os.environ.get("ANDROID_HOME") or os.environ.get("ANDROID_SDK_ROOT")
+                adb = str(Path(sdk) / "platform-tools/adb") if sdk else shutil.which("adb")
+                if not adb:
+                    raise RuntimeError("adb is required for --device")
+                report["consumers"][mode]["runtime"] = device_check(adb, args.device, consumer, mode, output / f"{mode}-device.log")
+        report["status"] = "passed"
+    except Exception as error:
+        report["status"] = "failed"
+        report["error"] = str(error)
+        raise
+    finally:
+        report_file.write_text(json.dumps(report, indent=2) + "\n")
+        print(f"Android consumer report: {report_file}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/packages/react-native/ReactShared/scripts/test-android-multipart.py b/packages/react-native/ReactShared/scripts/test-android-multipart.py
new file mode 100755
index 000000000000..54dd21744f73
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-android-multipart.py
@@ -0,0 +1,134 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""Run the real Android multipart adapter's JVM tests without building ReactAndroid.
+
+An optional benchmark compares the adapter with an explicitly selected native Git
+baseline. This measures a host JVM, not Android ART or network throughput.
+"""
+
+import argparse
+import json
+import pathlib
+import re
+import shutil
+import subprocess
+import tomllib
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--output", type=pathlib.Path)
+    parser.add_argument("--baseline-ref", help="Git revision of the native adapter")
+    parser.add_argument("--benchmark", action="store_true")
+    parser.add_argument("--offline", action="store_true")
+    parser.add_argument("--max-workers", type=int, default=2)
+    args = parser.parse_args()
+    if args.benchmark and not args.baseline_ref:
+        parser.error("--benchmark requires an explicit --baseline-ref")
+
+    shared = pathlib.Path(__file__).resolve().parents[1]
+    react_native = shared.parent
+    repo = react_native.parents[1]
+    adapter = react_native / "ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.kt"
+    tests = react_native / "ReactAndroid/src/test/java/com/facebook/react/devsupport/MultipartStreamReaderTest.kt"
+    if not tests.is_file():
+        parser.error("This fixture requires a React Native repository checkout; Android test sources are not included in the npm package.")
+    versions = tomllib.loads((react_native / "gradle/libs.versions.toml").read_text())["versions"]
+    language_version = ".".join(versions["kotlin"].split(".")[:2])
+    output = (args.output or shared / "build/android-multipart-test").resolve()
+    output.mkdir(parents=True, exist_ok=True)
+    gradle = [str(shared / "gradlew"), "--console=plain", f"--max-workers={args.max_workers}"]
+    if args.offline:
+        gradle.append("--offline")
+    subprocess.run(gradle + ["-p", str(shared), "exportAndroidJar"], check=True)
+
+    version = re.search(r'kotlin\("multiplatform"\) version "([^"]+)"', (shared / "build.gradle.kts").read_text())
+    if not version:
+        raise RuntimeError("Could not find the shared module's Kotlin compiler version")
+    (output / "settings.gradle.kts").write_text('''
+pluginManagement {
+  resolutionStrategy { eachPlugin {
+    if (requested.id.id == "org.jetbrains.kotlin.jvm")
+      useModule("org.jetbrains.kotlin:kotlin-gradle-plugin:${requested.version}")
+  } }
+  repositories { mavenCentral(); gradlePluginPortal() }
+}
+dependencyResolutionManagement { repositories { mavenCentral() } }
+rootProject.name = "multipart-adapter-tests"
+''')
+    # Keep the standalone compiler compatible with its Gradle wrapper while
+    # matching ReactAndroid's language/API level and runtime dependencies.
+    (output / "gradle.properties").write_text("kotlin.stdlib.default.dependency=false\n")
+    (output / "build.gradle.kts").write_text('''
+import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
+
+plugins { kotlin("jvm") version %s }
+kotlin {
+  jvmToolchain(17)
+  compilerOptions {
+    languageVersion.set(KotlinVersion.fromVersion(%s))
+    apiVersion.set(KotlinVersion.fromVersion(%s))
+  }
+}
+sourceSets {
+  main { kotlin.srcDir("main") }
+  test { kotlin.srcDir("test") }
+}
+dependencies {
+  implementation(files(%s))
+  implementation("org.jetbrains.kotlin:kotlin-stdlib:%s")
+  implementation("com.squareup.okio:okio:%s")
+  testImplementation("junit:junit:%s")
+  testImplementation("org.assertj:assertj-core:%s")
+}
+tasks.test { testLogging { events("passed", "failed", "skipped") } }
+tasks.register<JavaExec>("benchmark") {
+  classpath = sourceSets.main.get().runtimeClasspath
+  mainClass.set("com.facebook.react.devsupport.AndroidMultipartBenchmarkKt")
+}
+''' % (json.dumps(version[1]), json.dumps(language_version), json.dumps(language_version),
+       json.dumps(str(shared / "build/android/react-native-shared.jar")),
+       versions["kotlin"], versions["okio"], versions["junit"], versions["assertj"]))
+
+    # Keep only this runner's generated fixture inputs when reusing an output path.
+    generated = {
+        "main": ("MultipartStreamReader.kt", "MultipartStreamReaderBaseline.kt", "AndroidMultipartBenchmark.kt"),
+        "test": ("MultipartStreamReaderTest.kt", "MultipartStreamReaderBaselineTest.kt"),
+    }
+    for name, files in generated.items():
+        directory = output / name
+        directory.mkdir(exist_ok=True)
+        for source in files:
+            (directory / source).unlink(missing_ok=True)
+    shutil.copyfile(adapter, output / "main" / adapter.name)
+    shutil.copyfile(tests, output / "test" / tests.name)
+    if args.baseline_ref:
+        baseline_commit = subprocess.check_output(
+            ["git", "rev-parse", "--verify", f"{args.baseline_ref}^{{commit}}"], cwd=repo, text=True
+        ).strip()
+        print(f"Native baseline: {baseline_commit}", flush=True)
+        baseline = subprocess.check_output(
+            ["git", "show", f"{baseline_commit}:{adapter.relative_to(repo)}"], cwd=repo, text=True
+        )
+        if "com.facebook.react.shared" in baseline:
+            raise RuntimeError("The selected baseline already uses shared Kotlin code")
+        (output / "main/MultipartStreamReaderBaseline.kt").write_text(
+            baseline.replace("MultipartStreamReader", "MultipartStreamReaderBaseline")
+        )
+        (output / "test/MultipartStreamReaderBaselineTest.kt").write_text(
+            tests.read_text().replace("MultipartStreamReader", "MultipartStreamReaderBaseline")
+        )
+        if args.benchmark:
+            shutil.copyfile(shared / "tests/AndroidMultipartBenchmark.kt", output / "main/AndroidMultipartBenchmark.kt")
+    subprocess.run(gradle + ["-p", str(output), "test"], check=True)
+    if args.benchmark:
+        # Keep test compilation/execution out of the measurement window.
+        subprocess.run(gradle + ["-p", str(output), "benchmark"], check=True)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/packages/react-native/ReactShared/scripts/test-apple-app.sh b/packages/react-native/ReactShared/scripts/test-apple-app.sh
new file mode 100755
index 000000000000..5a849575d57a
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-apple-app.sh
@@ -0,0 +1,268 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -euo pipefail
+
+platform="${1:-simulator}"
+case "$platform" in
+  simulator|device|catalyst) ;;
+  *) echo 'usage: test-apple-app.sh [simulator|device|catalyst] [--prepare-only]' >&2; exit 1 ;;
+esac
+if [[ $# -gt 2 || ( $# -eq 2 && "$2" != --prepare-only ) ]]; then
+  echo 'error: The only optional second argument is --prepare-only.' >&2
+  exit 1
+fi
+
+shared_root="$(cd "$(dirname "$0")/.." && pwd)"
+repo_root="$(cd "$shared_root/../../.." && pwd)"
+original="$repo_root/packages/rn-tester"
+if [[ ! -f "$original/Podfile" ]]; then
+  echo 'error: This application test requires a React Native repository checkout with RNTester.' >&2
+  exit 1
+fi
+output="${RCT_KMP_APP_OUTPUT_DIR:-$shared_root/build/apple-app-$platform-${USE_FRAMEWORKS:-libraries}}"
+mkdir -p "$output"
+output="$(cd "$output" && pwd)"
+if [[ -e "$output/DerivedData" || -e "$output/Tests.xcresult" ]]; then
+  echo 'error: Choose a fresh RCT_KMP_APP_OUTPUT_DIR; existing products must not count as this run.' >&2
+  exit 1
+fi
+# A sibling preserves RNTester's relative references to the other packages.
+fixture="$(mktemp -d "$repo_root/packages/.rn-tester-kmp.XXXXXX")"
+simulator=""
+metro_pid=""
+websocket_pid=""
+cleanup() {
+  result=$?
+  trap - EXIT ERR
+  set +e
+  for pid in "$metro_pid" "$websocket_pid"; do
+    if [[ -n "$pid" ]]; then kill "$pid" 2>/dev/null; wait "$pid" 2>/dev/null; fi
+  done
+  if [[ -n "$simulator" ]]; then
+    xcrun simctl shutdown "$simulator" >/dev/null 2>&1
+    xcrun simctl delete "$simulator" >/dev/null 2>&1
+  fi
+  # Keep the generated configuration for diagnosis, without leaving a second app project.
+  cp "$fixture/Podfile" "$output/Podfile" 2>/dev/null
+  cp "$fixture/Podfile.lock" "$output/Podfile.lock" 2>/dev/null
+  cp "$fixture/package.json" "$output/package.json" 2>/dev/null
+  cp "$fixture/RNTesterPods.xcodeproj/project.pbxproj" "$output/project.pbxproj" 2>/dev/null
+  rm -rf "$fixture"
+  exit "$result"
+}
+trap cleanup EXIT
+trap 'exit 130' INT
+trap 'exit 143' TERM
+trap 'echo "error: RNTester validation failed; logs: $output" >&2' ERR
+
+rsync -a --exclude Pods --exclude build --exclude node_modules --exclude .xcode.env.local \
+  "$original/" "$fixture/"
+if [[ -d "$original/node_modules" ]]; then
+  ln -s "$original/node_modules" "$fixture/node_modules"
+fi
+# The source dependency graph can differ from the normally prebuilt Podfile.lock.
+rm -f "$fixture/Podfile.lock"
+python3 - "$fixture/Podfile" "$platform" <<'PY'
+import pathlib
+import json
+import sys
+
+podfile = pathlib.Path(sys.argv[1])
+# The copy must not introduce a duplicate workspace package when Metro follows
+# node_modules symlinks while bundling the original or copied app.
+package_path = podfile.parent / 'package.json'
+package = json.loads(package_path.read_text())
+package['name'] = '@react-native/tester-kmp-' + podfile.parent.name.rsplit('.', 1)[1].lower()
+package_path.write_text(json.dumps(package, indent=2) + '\n')
+source = podfile.read_text()
+if sys.argv[2] == 'catalyst':
+    setting = ':mac_catalyst_enabled => false'
+    if source.count(setting) != 1:
+        sys.exit('error: RNTester Catalyst setting changed; update the fixture.')
+    source = source.replace(setting, ':mac_catalyst_enabled => true')
+podfile.write_text(source)
+PY
+if [[ "${2:-}" == --prepare-only ]]; then
+  echo "RNTester $platform fixture prepared successfully; no dependencies, builds or tests were run."
+  exit 0
+fi
+
+export RCT_USE_KMP=1 RCT_USE_PREBUILT_RNCORE=0 RCT_USE_RN_DEP=0
+export RCT_NO_LAUNCH_PACKAGER=1
+export NODE_BINARY="$(command -v node)"
+# Use the same bundle for the repository check and the copied app's Podfile.
+export BUNDLE_GEMFILE="${BUNDLE_GEMFILE:-$repo_root/Gemfile}"
+cd "$repo_root"
+bundle check > "$output/bundle-check.log" 2>&1
+if [[ "$platform" == catalyst ]]; then
+  # Xcode selects destinations before applying command-line build settings.
+  # Enable Catalyst in the copied application project as well as in its pods.
+  bundle exec ruby - "$fixture/RNTesterPods.xcodeproj" <<'RUBY'
+require 'xcodeproj'
+project = Xcodeproj::Project.open(ARGV.fetch(0))
+project.targets.each do |target|
+  target.build_configurations.each do |configuration|
+    configuration.build_settings['SUPPORTS_MACCATALYST'] = 'YES'
+  end
+end
+project.save
+RUBY
+fi
+yarn --cwd packages/react-native-codegen build > "$output/codegen.log" 2>&1
+cd "$fixture"
+bundle exec pod install > "$output/pod-install.log" 2>&1
+
+build=(xcodebuild -workspace "$fixture/RNTesterPods.xcworkspace" -scheme RNTester
+  -derivedDataPath "$output/DerivedData" -jobs "${RCT_KMP_APP_JOBS:-4}" CODE_SIGNING_ALLOWED=NO)
+if [[ "$platform" == simulator ]]; then
+  # Own the servers and simulator so cleanup never stops a developer's processes.
+  for port in 8081 5555; do
+    if lsof -n -iTCP:"$port" -sTCP:LISTEN >/dev/null 2>&1; then
+      echo "error: Port $port is in use; stop its server before running the application test." >&2
+      exit 1
+    fi
+  done
+  cd "$original"
+  "$repo_root/node_modules/.bin/react-native" start --max-workers 2 > "$output/metro.log" 2>&1 &
+  metro_pid=$!
+  node IntegrationTests/websocket_integration_test_server.js > "$output/websocket.log" 2>&1 &
+  websocket_pid=$!
+  ready=0
+  for ((attempt=0; attempt<60; attempt++)); do
+    if curl --silent --fail --max-time 1 http://localhost:8081/status | grep -q 'packager-status:running' && \
+        curl --silent --max-time 1 http://localhost:5555 | grep -q 'Upgrade Required'; then ready=1; break; fi
+    sleep 1
+  done
+  if [[ "$ready" != 1 ]]; then echo 'error: Test servers did not become ready.' >&2; exit 1; fi
+  curl --silent --show-error --fail \
+    'http://localhost:8081/js/RNTesterApp.bundle?platform=ios&dev=true' -o "$output/RNTesterApp.bundle"
+  xcrun simctl list -j > "$output/simulators.json"
+  read -r device_type runtime < <(python3 - "$output/simulators.json" <<'PY'
+import json
+import sys
+
+state = json.load(open(sys.argv[1]))
+runtimes = [item for item in state['runtimes'] if item.get('isAvailable') and '.iOS-' in item['identifier']]
+if not runtimes:
+    sys.exit('error: Install an iOS Simulator runtime before running application tests.')
+for runtime in sorted(runtimes, key=lambda item: tuple(map(int, item['version'].split('.'))), reverse=True):
+    devices = [item for item in state['devices'].get(runtime['identifier'], [])
+               if item.get('isAvailable') and item['name'].startswith('iPhone') and item.get('deviceTypeIdentifier')]
+    if devices:
+        print(devices[0]['deviceTypeIdentifier'], runtime['identifier'])
+        break
+else:
+    sys.exit('error: Create an available iPhone simulator in Xcode before running application tests.')
+PY
+)
+  simulator="$(xcrun simctl create 'React Native KMP application test' "$device_type" "$runtime")"
+  xcrun simctl boot "$simulator"
+  xcrun simctl bootstatus "$simulator" -b
+  "${build[@]}" test -configuration Debug -sdk iphonesimulator \
+    -destination "platform=iOS Simulator,id=$simulator" -parallel-testing-enabled NO \
+    -resultBundlePath "$output/Tests.xcresult" > "$output/xcodebuild.log" 2>&1
+  xcrun xcresulttool get test-results summary --path "$output/Tests.xcresult" > "$output/test-summary.json"
+  python3 - "$output/test-summary.json" <<'PY'
+import json
+import sys
+
+summary = json.load(open(sys.argv[1]))
+if summary.get('failedTests', 0) or not summary.get('passedTests', 0):
+    sys.exit('error: RNTester must execute passing tests; an empty test run is not validation.')
+PY
+  # The existing test plan enables sanitizers, so Xcode may add a Variant-ASan-UBSan directory.
+  product="$(python3 - "$output/DerivedData/Build/Products" <<'PY'
+import pathlib
+import sys
+
+apps = list(pathlib.Path(sys.argv[1]).glob('**/Debug-iphonesimulator/RNTester.app'))
+if len(apps) != 1:
+    sys.exit(f'error: Expected one tested RNTester.app, found {apps}; use a fresh output directory.')
+print(apps[0])
+PY
+)"
+  identifier=$(/usr/libexec/PlistBuddy -c 'Print CFBundleIdentifier' "$product/Info.plist")
+  xcrun simctl install "$simulator" "$product"
+  xcrun simctl launch --terminate-running-process "$simulator" "$identifier" > "$output/app-launch.log" 2>&1
+elif [[ "$platform" == device ]]; then
+  "${build[@]}" build -configuration Release -sdk iphoneos -destination 'generic/platform=iOS' \
+    > "$output/xcodebuild.log" 2>&1
+else
+  "${build[@]}" build -configuration Debug -destination 'generic/platform=macOS,variant=Mac Catalyst' \
+    SUPPORTS_MACCATALYST=YES > "$output/xcodebuild.log" 2>&1
+fi
+
+# Check the actual object compiled by the pod target: just finding Kotlin in the
+# app would not prove that each adapter selected the shared implementation.
+python3 - "$output/DerivedData" "$platform" "$output/shared-adapter-symbols.txt" <<'PY'
+import pathlib
+import subprocess
+import sys
+
+expected_kmp = sys.argv[2] != 'catalyst'
+reports = []
+for filename, classes in (
+    ('RCTGradientUtils.o', ('RNSGradientStops',)),
+    ('RCTEnhancedScrollView.o', ('RNSScrollSnapOffsets',)),
+    ('RCTMultipartStreamReader.o', ('RNSMultipartFraming', 'RNSMultipartHeaders')),
+):
+    objects = list(pathlib.Path(sys.argv[1]).rglob(filename))
+    if not objects:
+        sys.exit(f'error: RNTester did not compile {filename} from source.')
+    symbols = [subprocess.check_output(['xcrun', 'nm', '-u', str(item)], text=True) for item in objects]
+    reports.extend([filename, *symbols])
+    for class_name in classes:
+        if any((f'OBJC_CLASS_$_{class_name}' in item) != expected_kmp for item in symbols):
+            sys.exit(f'error: {filename} selected an unexpected implementation for {class_name}.')
+pathlib.Path(sys.argv[3]).write_text('\n'.join(reports))
+PY
+if [[ "$platform" == simulator ]]; then
+  # Hosted test bundles must resolve Kotlin classes through their app, even when
+  # their Podfile target independently declares the same pods. Standalone tests
+  # run in a different process and may link their own runtime.
+  python3 - "$product" "$output/shared-runtime-ownership.json" <<'PY'
+import json
+import pathlib
+import plistlib
+import subprocess
+import sys
+
+app = pathlib.Path(sys.argv[1])
+def executable(bundle):
+    with (bundle / 'Info.plist').open('rb') as info:
+        return bundle / plistlib.load(info)['CFBundleExecutable']
+
+def owns_runtime(binary):
+    symbols = subprocess.check_output(['xcrun', 'nm', '-gU', str(binary)], text=True)
+    return any(line.endswith(' _OBJC_CLASS_$_RNSBase') for line in symbols.splitlines())
+
+main = executable(app)
+candidates = [main, app / (main.name + '.debug.dylib')]
+candidates.extend(executable(bundle) for bundle in (app / 'Frameworks').glob('*.framework'))
+owners = [binary for binary in candidates if binary.exists() and owns_runtime(binary)]
+if len(owners) != 1:
+    sys.exit(f'error: Expected one shared runtime owner in RNTester, found {owners}')
+owner = owners[0]
+hosted = []
+for bundle in (app / 'PlugIns').glob('*.xctest'):
+    if owns_runtime(executable(bundle)):
+        sys.exit(f'error: Hosted test bundle duplicates the app shared runtime: {bundle}')
+    # CocoaPods may also package an identical dynamic framework for XCTest.
+    for framework in (bundle / 'Frameworks').glob('*.framework'):
+        copy = executable(framework)
+        if owns_runtime(copy) and (framework.name != owner.parent.name or copy.read_bytes() != owner.read_bytes()):
+            sys.exit(f'error: Hosted test bundle has a different shared runtime framework: {copy}')
+    hosted.append(str(bundle.relative_to(app)))
+pathlib.Path(sys.argv[2]).write_text(json.dumps({
+    'runtimeOwner': str(owner.relative_to(app)),
+    'hostedBundlesWithoutOwnRuntime': hosted,
+}, indent=2) + '\n')
+PY
+  echo "RNTester tests and simulator launch passed (${USE_FRAMEWORKS:-static libraries}); reports: $output"
+else
+  echo "RNTester $platform unsigned build passed; no device tests were run. Reports: $output"
+fi
diff --git a/packages/react-native/ReactShared/scripts/test-apple-distribution.sh b/packages/react-native/ReactShared/scripts/test-apple-distribution.sh
new file mode 100755
index 000000000000..b33c93fcdbfa
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-apple-distribution.sh
@@ -0,0 +1,117 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -euo pipefail
+
+mode="${1:-}"
+case "$mode" in
+  ''|--build-only|--package-only) ;;
+  *) echo "Usage: $0 [--build-only|--package-only]" >&2; exit 1 ;;
+esac
+shared_root="$(cd "$(dirname "$0")/.." && pwd)"
+build_type="${RCT_KMP_BUILD_TYPE:-Release}"
+case "$build_type" in
+  Debug) variant=debugFramework ;;
+  Release) variant=releaseFramework ;;
+  *) echo 'error: RCT_KMP_BUILD_TYPE must be Debug or Release.' >&2; exit 1 ;;
+esac
+output="${RCT_KMP_DISTRIBUTION_OUTPUT_DIR:-$shared_root/build/apple-distribution/$build_type}"
+mkdir -p "$output"
+output="$(cd "$output" && pwd)"
+# A fresh fixture avoids stale architecture slices or outputs from another build.
+fixture="$(mktemp -d "$output/consumer.XXXXXX")"
+cp -R "$shared_root/tests/distribution/." "$fixture/"
+
+if [[ "$mode" != --package-only ]]; then
+  "$shared_root/gradlew" -p "$shared_root" --console=plain \
+    "link${build_type}FrameworkIosArm64" \
+    "link${build_type}FrameworkIosSimulatorArm64" \
+    "link${build_type}FrameworkIosX64"
+fi
+
+device="$shared_root/build/bin/iosArm64/$variant/ReactNativeShared.framework"
+sim_arm="$shared_root/build/bin/iosSimulatorArm64/$variant/ReactNativeShared.framework"
+sim_intel="$shared_root/build/bin/iosX64/$variant/ReactNativeShared.framework"
+for framework in "$device" "$sim_arm" "$sim_intel"; do
+  test -f "$framework/ReactNativeShared"
+  cmp "$device/Headers/ReactNativeShared.h" "$framework/Headers/ReactNativeShared.h"
+done
+ditto "$sim_arm" "$fixture/simulator/ReactNativeShared.framework"
+xcrun lipo -create "$sim_arm/ReactNativeShared" "$sim_intel/ReactNativeShared" \
+  -output "$fixture/simulator/ReactNativeShared.framework/ReactNativeShared"
+xcodebuild -create-xcframework -framework "$device" \
+  -framework "$fixture/simulator/ReactNativeShared.framework" \
+  -output "$fixture/ReactNativeShared.xcframework" > "$fixture/package.log" 2>&1
+
+# Include the matching Kotlin runtime's license bundle in any packaged experiment.
+python3 - "$shared_root" "$fixture" "$mode" <<'PY'
+import hashlib, json, os, pathlib, platform, plistlib, re, shutil, sys
+root, fixture = map(pathlib.Path, sys.argv[1:3])
+compiler = re.search(r'version "([^"]+)"', (root / 'build.gradle.kts').read_text())[1]
+host = 'aarch64' if platform.machine() == 'arm64' else 'x86_64'
+konan = pathlib.Path(os.environ.get('KONAN_DATA_DIR', pathlib.Path.home() / '.konan'))
+native_home = pathlib.Path(os.environ.get('KONAN_HOME', konan / f'kotlin-native-prebuilt-macos-{host}-{compiler}'))
+licenses = native_home / 'licenses'
+if not (licenses / 'LICENSE.txt').is_file():
+    sys.exit(f'error: Matching Kotlin {compiler} licenses missing at {licenses}; set KONAN_HOME.')
+shutil.copytree(licenses, fixture / 'licenses' / 'kotlin')
+shutil.copyfile(root.parent / 'LICENSE', fixture / 'licenses' / 'ReactNative-LICENSE')
+xcf = fixture / 'ReactNativeShared.xcframework'
+info = plistlib.loads((xcf / 'Info.plist').read_bytes())
+slices = {(item['SupportedPlatform'], item.get('SupportedPlatformVariant', ''),
+           tuple(sorted(item['SupportedArchitectures']))) for item in info['AvailableLibraries']}
+expected = {('ios', '', ('arm64',)), ('ios', 'simulator', ('arm64', 'x86_64'))}
+if slices != expected:
+    sys.exit(f'error: Unexpected XCFramework slices: {slices}')
+manifest = {
+    'kotlinVersion': compiler,
+    'reusedExistingFrameworks': sys.argv[3] == '--package-only',
+    'files': {str(p.relative_to(fixture)): hashlib.sha256(p.read_bytes()).hexdigest()
+              for p in sorted(xcf.rglob('*')) if p.is_file()},
+    'scope': 'Isolated binary consumer; not the React Native core SwiftPM/prebuilt integration',
+}
+(fixture / 'distribution.json').write_text(json.dumps(manifest, indent=2) + '\n')
+PY
+
+if [[ "$mode" == --package-only ]]; then
+  echo "XCFramework slices and licenses checked using existing frameworks; consumer build/execution pending: $fixture"
+  exit 0
+fi
+
+(cd "$fixture" && swift package describe --type json) > "$fixture/package-description.json" 2> "$fixture/package-description.log"
+for platform in 'iOS' 'iOS Simulator' 'macOS,variant=Mac Catalyst'; do
+  name="${platform// /-}"
+  (cd "$fixture" && xcodebuild -scheme KMPDistributionProbe \
+    -destination "generic/platform=$platform" -derivedDataPath "$fixture/derived/$name" \
+    -configuration "$build_type" CLANG_ENABLE_CODE_COVERAGE=NO CODE_SIGNING_ALLOWED=NO build) > "$fixture/$name.log" 2>&1
+done
+if [[ "$mode" != --build-only ]]; then
+  simulator="${RCT_KMP_SIMULATOR_UDID:-}"
+  if [[ -z "$simulator" ]]; then
+    simulator="$(xcrun simctl list devices available -j | python3 -c '
+import json, sys
+for runtime, devices in json.load(sys.stdin)["devices"].items():
+    if ".iOS-" in runtime and devices:
+        print(devices[0]["udid"])
+        break
+')"
+  fi
+  : "${simulator:?Install an iOS simulator runtime or set RCT_KMP_SIMULATOR_UDID}"
+  (cd "$fixture" && xcodebuild -scheme KMPDistributionProbe \
+    -destination "id=$simulator" -derivedDataPath "$fixture/derived/iOS-Simulator" \
+    -configuration "$build_type" -resultBundlePath "$fixture/consumer.xcresult" \
+    -enableCodeCoverage NO CODE_SIGNING_ALLOWED=NO test) > "$fixture/consumer-test.log" 2>&1
+  xcrun xcresulttool get test-results summary --path "$fixture/consumer.xcresult" > "$fixture/test-summary.json"
+  python3 - "$fixture/test-summary.json" <<'PY'
+import json
+import sys
+
+summary = json.load(open(sys.argv[1]))
+if summary.get('failedTests', 0) or not summary.get('passedTests', 0):
+    sys.exit('error: The distribution consumer must execute passing tests.')
+PY
+fi
+echo "Apple distribution checks completed ($mode): $fixture"
diff --git a/packages/react-native/ReactShared/scripts/test-apple-gradient.sh b/packages/react-native/ReactShared/scripts/test-apple-gradient.sh
new file mode 100755
index 000000000000..76546496098c
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-apple-gradient.sh
@@ -0,0 +1,119 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -euo pipefail
+
+shared_root="$(cd "$(dirname "$0")/.." && pwd)"
+react_native_root="$(cd "$shared_root/.." && pwd)"
+test_root="${RCT_KMP_TEST_OUTPUT_DIR:-$shared_root/build/apple-gradient-test}"
+architecture="$(uname -m)"
+sdk_root="$(xcrun --sdk iphonesimulator --show-sdk-path)"
+mkdir -p "$test_root/include/React"
+
+# Build and stage through the same helper that the CocoaPods build phase uses.
+PLATFORM_NAME=iphonesimulator ARCHS="$architecture" CONFIGURATION=Debug \
+  PODS_CONFIGURATION_BUILD_DIR="$test_root" "$shared_root/scripts/build-apple-framework.sh"
+
+for header in "$react_native_root"/React/Base/*.h; do
+  ln -sf "$header" "$test_root/include/React/$(basename "$header")"
+done
+ln -sf "$react_native_root/Libraries/NativeAnimation/RCTAnimationUtils.h" "$test_root/include/React/RCTAnimationUtils.h"
+ln -sf "$react_native_root/React/Fabric/Utils/RCTGradientUtils.h" "$test_root/include/React/RCTGradientUtils.h"
+
+# Use the real inline color conversion without pulling unrelated renderer/Folly
+# headers into this standalone test. Fail if its declaration can no longer be extracted.
+python3 - "$react_native_root/React/Fabric/RCTConversions.h" "$test_root/include/React/RCTConversions.h" <<'PY'
+import pathlib
+import re
+import sys
+
+source = pathlib.Path(sys.argv[1]).read_text()
+helpers = re.findall(
+    r"(?m)^inline UIColor \*_Nullable RCTUIColorFromSharedColor\([^\n]*\)\n\{[^{}]*\n\}", source
+)
+if len(helpers) != 1:
+    sys.exit("error: RCTUIColorFromSharedColor changed; update the standalone parity header extraction.")
+pathlib.Path(sys.argv[2]).write_text(
+    "#import <react/renderer/graphics/Color.h>\n"
+    "#import <react/renderer/graphics/RCTPlatformColorUtils.h>\n" + helpers[0] + "\n"
+)
+PY
+
+graphics="$react_native_root/ReactCommon/react/renderer/graphics"
+ios_graphics="$graphics/platform/ios/react/renderer/graphics"
+flags=(
+  -std=c++20 -fobjc-arc -DREACT_NATIVE_PRODUCTION -DRCTLOG_ENABLED=0 -include memory -include vector
+  -target "$architecture-apple-ios15.1-simulator" -isysroot "$sdk_root"
+  -I "$test_root/include" -I "$react_native_root/ReactCommon" -I "$graphics/platform/ios"
+  -F "$test_root/ReactNativeSharedKMP"
+)
+if [[ "${RCT_KMP_BUILD_TYPE:-Debug}" == "Release" ]]; then
+  flags+=(-O2)
+fi
+adapter="$react_native_root/React/Fabric/Utils/RCTGradientUtils.mm"
+xcrun clang++ "${flags[@]}" -DRCT_USE_KMP=1 -c "$adapter" -o "$test_root/adapter.o"
+xcrun clang++ "${flags[@]}" -DRCT_USE_KMP=0 -DRCTGradientUtils=RCTGradientUtilsBaseline \
+  -c "$adapter" -o "$test_root/baseline.o"
+native_sources=(
+  "$react_native_root/Libraries/NativeAnimation/RCTAnimationUtils.mm"
+  "$graphics/Color.cpp" "$graphics/ColorComponents.cpp"
+  "$ios_graphics/HostPlatformColor.mm" "$ios_graphics/RCTPlatformColorUtils.mm"
+  "$react_native_root/ReactCommon/react/utils/ManagedObjectWrapper.mm"
+)
+native_objects=()
+for source in "${native_sources[@]}"; do
+  object="$test_root/$(basename "$source").o"
+  xcrun clang++ "${flags[@]}" -x objective-c++ -c "$source" -o "$object"
+  native_objects+=("$object")
+done
+frameworks=(-framework Foundation -framework UIKit -framework QuartzCore -framework CoreGraphics)
+xcrun clang++ "${flags[@]}" "$shared_root/tests/AppleGradientParity.mm" \
+  "$test_root/adapter.o" "$test_root/baseline.o" "${native_objects[@]}" \
+  -framework ReactNativeShared "${frameworks[@]}" \
+  -o "$test_root/AppleGradientParity"
+
+# Exercise the dynamic RCTFabric linkage model too: Kotlin is linked into this
+# library only, and the caller links the library without another Kotlin runtime.
+xcrun clang++ "${flags[@]}" -dynamiclib "$test_root/adapter.o" "${native_objects[@]}" \
+  -framework ReactNativeShared "${frameworks[@]}" \
+  -Wl,-install_name,@rpath/libKMPGradientAdapter.dylib -o "$test_root/libKMPGradientAdapter.dylib"
+xcrun clang++ "${flags[@]}" "$shared_root/tests/AppleGradientParity.mm" "$test_root/baseline.o" \
+  -L "$test_root" -lKMPGradientAdapter "${frameworks[@]}" -Wl,-rpath,"$test_root" \
+  -o "$test_root/AppleGradientParityDynamic"
+
+# Catalyst must compile the original path even when the pilot flag is defined,
+# without a framework header search path or a nonexistent Catalyst K/N slice.
+mac_sdk_root="$(xcrun --sdk macosx --show-sdk-path)"
+xcrun clang++ -std=c++20 -fobjc-arc -DREACT_NATIVE_PRODUCTION -DRCT_USE_KMP=1 \
+  -target "$architecture-apple-ios15.1-macabi" -isysroot "$mac_sdk_root" \
+  -isystem "$mac_sdk_root/System/iOSSupport/usr/include" \
+  -iframework "$mac_sdk_root/System/iOSSupport/System/Library/Frameworks" \
+  -include memory -include vector -I "$test_root/include" \
+  -I "$react_native_root/ReactCommon" -I "$graphics/platform/ios" -fsyntax-only "$adapter"
+
+if [[ "${RCT_KMP_BUILD_ONLY:-0}" == "1" ]]; then
+  echo "Apple gradient harnesses compiled; execution was not requested: $test_root"
+  exit 0
+fi
+
+simulator="${RCT_KMP_SIMULATOR_UDID:-}"
+if [[ -z "$simulator" ]]; then
+  simulator="$(xcrun simctl list devices available -j | python3 -c '
+import json, sys
+devices = json.load(sys.stdin)["devices"]
+for runtime, entries in devices.items():
+    if ".iOS-" in runtime and entries:
+        print(entries[0]["udid"])
+        break
+')"
+fi
+if [[ -z "$simulator" ]]; then
+  echo 'error: Install an iOS Simulator runtime in Xcode before running the Apple gradient parity test.' >&2
+  exit 1
+fi
+# Standalone spawn runs the executable without booting or modifying the simulator.
+xcrun simctl spawn --standalone "$simulator" "$test_root/AppleGradientParity"
+xcrun simctl spawn --standalone "$simulator" "$test_root/AppleGradientParityDynamic"
diff --git a/packages/react-native/ReactShared/scripts/test-apple-multipart.sh b/packages/react-native/ReactShared/scripts/test-apple-multipart.sh
new file mode 100755
index 000000000000..ce6bce09acb2
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-apple-multipart.sh
@@ -0,0 +1,95 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -euo pipefail
+
+shared_root="$(cd "$(dirname "$0")/.." && pwd)"
+react_native_root="$(cd "$shared_root/.." && pwd)"
+repo_root="$(cd "$react_native_root/../.." && pwd)"
+tests="$repo_root/packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m"
+if [[ ! -f "$tests" ]]; then
+  echo 'error: This fixture requires a React Native repository checkout with RNTester test sources.' >&2
+  exit 1
+fi
+test_root="${RCT_KMP_TEST_OUTPUT_DIR:-$shared_root/build/apple-multipart-test}"
+architecture="$(uname -m)"
+sdk_root="$(xcrun --sdk iphonesimulator --show-sdk-path)"
+developer="$(xcode-select -p)/Platforms/iPhoneSimulator.platform/Developer"
+mkdir -p "$test_root/include/React"
+ln -sf "$react_native_root/React/Base/RCTMultipartStreamReader.h" "$test_root/include/React/RCTMultipartStreamReader.h"
+
+PLATFORM_NAME=iphonesimulator ARCHS="$architecture" CONFIGURATION=Release \
+  PODS_CONFIGURATION_BUILD_DIR="$test_root" "$shared_root/scripts/build-apple-framework.sh"
+
+flags=(
+  -fobjc-arc -O2 -target "$architecture-apple-ios15.1-simulator" -isysroot "$sdk_root"
+  -I "$test_root/include" -F "$test_root/ReactNativeSharedKMP"
+)
+adapter="$react_native_root/React/Base/RCTMultipartStreamReader.m"
+xcrun clang "${flags[@]}" -DRCT_USE_KMP=1 -c "$adapter" -o "$test_root/adapter.o"
+xcrun clang "${flags[@]}" -DRCT_USE_KMP=0 -DRCTMultipartStreamReader=RCTMultipartStreamReaderBaseline \
+  -c "$adapter" -o "$test_root/baseline.o"
+
+# Check that the opt-in actually calls the shared framing/header types.
+nm -u "$test_root/adapter.o" | grep -q 'OBJC_CLASS_\$_RNSMultipartFraming'
+nm -u "$test_root/adapter.o" | grep -q 'OBJC_CLASS_\$_RNSMultipartHeaders'
+if nm -u "$test_root/baseline.o" | grep -q 'OBJC_CLASS_\$_RNS'; then
+  echo 'error: Native fallback unexpectedly references Kotlin classes.' >&2
+  exit 1
+fi
+
+# Compile the actual RNTester XCTest source, then run the same tests on both paths.
+for mode in native kmp; do
+  bundle="$test_root/Multipart-$mode.xctest"
+  mkdir -p "$bundle"
+  use_kmp=0
+  if [[ "$mode" == kmp ]]; then use_kmp=1; fi
+  xcrun clang "${flags[@]}" -DRCT_USE_KMP="$use_kmp" -bundle \
+    -F "$developer/Library/Frameworks" -framework XCTest \
+    -Wl,-rpath,"$developer/Library/Frameworks" \
+    "$adapter" "$tests" \
+    -framework Foundation -framework QuartzCore -framework ReactNativeShared -o "$bundle/MultipartTests"
+  /usr/libexec/PlistBuddy -c Clear "$bundle/Info.plist" >/dev/null
+  /usr/libexec/PlistBuddy -c 'Add :CFBundleExecutable string MultipartTests' "$bundle/Info.plist"
+  /usr/libexec/PlistBuddy -c 'Add :CFBundleIdentifier string com.facebook.react.MultipartTests' "$bundle/Info.plist"
+  /usr/libexec/PlistBuddy -c 'Add :CFBundlePackageType string BNDL' "$bundle/Info.plist"
+done
+
+xcrun clang "${flags[@]}" "$shared_root/tests/AppleMultipartParity.m" \
+  "$test_root/adapter.o" "$test_root/baseline.o" \
+  -framework Foundation -framework QuartzCore -framework ReactNativeShared -o "$test_root/AppleMultipartParity"
+
+# Catalyst keeps the Foundation implementation, including when opt-in is set.
+mac_sdk_root="$(xcrun --sdk macosx --show-sdk-path)"
+xcrun clang -fobjc-arc -DRCT_USE_KMP=1 \
+  -target "$architecture-apple-ios15.1-macabi" -isysroot "$mac_sdk_root" \
+  -isystem "$mac_sdk_root/System/iOSSupport/usr/include" \
+  -iframework "$mac_sdk_root/System/iOSSupport/System/Library/Frameworks" \
+  -fsyntax-only "$adapter"
+
+if [[ "${RCT_KMP_BUILD_ONLY:-0}" == "1" ]]; then exit 0; fi
+simulator="${RCT_KMP_SIMULATOR_UDID:-}"
+if [[ -z "$simulator" ]]; then
+  simulator="$(xcrun simctl list devices available -j | python3 -c '
+import json, sys
+for runtime, entries in json.load(sys.stdin)["devices"].items():
+    if ".iOS-" in runtime and entries:
+        print(entries[0]["udid"])
+        break
+')"
+fi
+if [[ -z "$simulator" ]]; then
+  echo 'error: Install an iOS Simulator runtime before running multipart tests.' >&2
+  exit 1
+fi
+for mode in native kmp; do
+  xcrun simctl spawn --standalone "$simulator" "$developer/Library/Xcode/Agents/xctest" \
+    "$test_root/Multipart-$mode.xctest"
+done
+xcrun simctl spawn --standalone "$simulator" "$test_root/AppleMultipartParity"
+if [[ "${RCT_KMP_BENCHMARK:-0}" == "1" ]]; then
+  xcrun simctl spawn --standalone "$simulator" "$test_root/AppleMultipartParity" --benchmark
+fi
diff --git a/packages/react-native/ReactShared/scripts/test-apple-scroll-snap.py b/packages/react-native/ReactShared/scripts/test-apple-scroll-snap.py
new file mode 100755
index 000000000000..925317278558
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-apple-scroll-snap.py
@@ -0,0 +1,184 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""Compile the real Apple scroll adapter in both modes, compare it, and measure Release calls.
+
+Uses an iOS simulator; does not build RNTester or change an existing simulator's state.
+Measurements are isolated simulator observations, not device interaction or app startup results.
+"""
+
+import argparse
+import hashlib
+import json
+import os
+import pathlib
+import platform
+import subprocess
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--output", type=pathlib.Path)
+    parser.add_argument("--build-only", action="store_true")
+    parser.add_argument("--benchmark-repeats", type=int, default=3)
+    args = parser.parse_args()
+    if not 0 <= args.benchmark_repeats <= 20:
+        parser.error("benchmark-repeats must be 0..20")
+    shared = pathlib.Path(__file__).resolve().parent.parent
+    react = shared.parent
+    output = (args.output or shared / "build/apple-scroll-snap").resolve()
+    output.mkdir(parents=True, exist_ok=False)
+    command_number = 0
+
+    def run(command, **kwargs):
+        nonlocal command_number
+        command_number += 1
+        result = subprocess.run(command, capture_output=True, text=True, **kwargs)
+        (output / f"command-{command_number}.log").write_text(
+            repr(command) + "\n" + result.stdout + result.stderr
+        )
+        if result.returncode:
+            raise RuntimeError(f"Command failed; see {output}/command-{command_number}.log\n{result.stderr[-4000:]}")
+        return result.stdout
+
+    architecture = platform.machine()
+    task_target = {"arm64": "IosSimulatorArm64", "x86_64": "IosX64"}[architecture]
+    native_target = {"arm64": "iosSimulatorArm64", "x86_64": "iosX64"}[architecture]
+    run([str(shared / "gradlew"), "-p", str(shared), f"linkReleaseFramework{task_target}",
+         "--max-workers=2", "--console=plain"])
+    framework_parent = shared / f"build/bin/{native_target}/releaseFramework"
+    include = output / "include/React"
+    include.mkdir(parents=True)
+    for header in (react / "React/Base").glob("*.h"):
+        (include / header.name).symlink_to(header)
+    scroll = react / "React/Fabric/Mounting/ComponentViews/ScrollView"
+    splitter = react / "React/Fabric/Utils"
+    for header in [scroll / "RCTEnhancedScrollView.h", splitter / "RCTGenericDelegateSplitter.h"]:
+        (include / header.name).symlink_to(header)
+    # EnhancedScrollView.h includes this header without using any of its declarations.
+    # Keep unrelated Fabric/Folly dependencies out of the standalone UIKit fixture.
+    (include / "RCTViewComponentView.h").write_text("// Unused transitive Fabric header in this standalone fixture.\n")
+    sdk = run(["xcrun", "--sdk", "iphonesimulator", "--show-sdk-path"]).strip()
+    flags = ["-std=c++20", "-O2", "-fobjc-arc", "-DREACT_NATIVE_PRODUCTION", "-DRCTLOG_ENABLED=0",
+             "-target", f"{architecture}-apple-ios15.1-simulator", "-isysroot", sdk,
+             "-I", str(output / "include"), "-I", str(react / "ReactCommon"), "-F", str(framework_parent)]
+    frameworks = ["-framework", "Foundation", "-framework", "UIKit", "-framework", "QuartzCore", "-framework", "CoreGraphics"]
+    adapter = scroll / "RCTEnhancedScrollView.mm"
+    harness = shared / "tests/AppleScrollSnapParity.mm"
+    splitter_object = output / "splitter.o"
+    run(["xcrun", "clang++", *flags, "-c", str(splitter / "RCTGenericDelegateSplitter.mm"), "-o", str(splitter_object)])
+    for mode, defines in {
+        "kmp": ["-DRCT_USE_KMP=1"],
+        "baseline": ["-DRCT_USE_KMP=0", "-DRCTEnhancedScrollView=RCTEnhancedScrollViewBaseline"],
+        "native": ["-DRCT_USE_KMP=0"],
+    }.items():
+        run(["xcrun", "clang++", *flags, *defines, "-c", str(adapter), "-o", str(output / f"{mode}.o")])
+    # Control for the benefit of caching alone: compile the actual native implementation
+    # with vector storage/access, leaving its selection algorithm unchanged. This staged
+    # file is a measurement fixture, never a production source edit.
+    cached_source = adapter.read_text()
+    edits = {
+        '#import "RCTEnhancedScrollView.h"': '#import <React/RCTEnhancedScrollView.h>\n#include <vector>',
+        '  BOOL _isSetContentOffsetDisabled;': '  BOOL _isSetContentOffsetDisabled;\n  std::vector<CGFloat> _cachedNativeOffsets;',
+        '}\n\n#if RCT_SCROLL_SNAP_USE_KMP\n@synthesize': '''}
+@synthesize snapToOffsets = _snapToOffsets;
+- (void)setSnapToOffsets:(NSArray<NSNumber *> *)snapToOffsets
+{
+  _snapToOffsets = [snapToOffsets copy];
+  _cachedNativeOffsets.clear();
+  _cachedNativeOffsets.reserve(_snapToOffsets.count);
+  for (NSNumber *offset in _snapToOffsets) {
+    _cachedNativeOffsets.push_back(offset.floatValue);
+  }
+}
+
+#if RCT_SCROLL_SNAP_USE_KMP
+@synthesize''',
+        'i < self.snapToOffsets.count': 'i < _cachedNativeOffsets.size()',
+        '[[self.snapToOffsets objectAtIndex:i] floatValue]': '_cachedNativeOffsets[i]',
+        '[[self.snapToOffsets firstObject] floatValue]': '_cachedNativeOffsets.front()',
+        '[[self.snapToOffsets lastObject] floatValue]': '_cachedNativeOffsets.back()',
+    }
+    for before, after in edits.items():
+        if cached_source.count(before) != 1:
+            raise RuntimeError(f"Native cache control requires review after adapter change: {before}")
+        cached_source = cached_source.replace(before, after)
+    cached_path = output / "CachedNativeScrollView.mm"
+    cached_path.write_text(cached_source)
+    for name, defines in {"cached": [], "cached-parity": ["-DRCTEnhancedScrollView=RCTEnhancedScrollViewCached"]}.items():
+        run(["xcrun", "clang++", *flags, "-DRCT_USE_KMP=0", *defines, "-c", str(cached_path), "-o", str(output / f"{name}.o")])
+    symbols = {mode: run(["xcrun", "nm", "-u", str(output / f"{mode}.o")]) for mode in ("kmp", "native")}
+    if "RNSScrollSnapOffsets" not in symbols["kmp"] or "RNS" in symbols["native"]:
+        raise RuntimeError("Compiled adapters did not use the expected KMP/native paths")
+    parity = output / "AppleScrollSnapParity"
+    run(["xcrun", "clang++", *flags, str(harness), str(output / "kmp.o"), str(output / "baseline.o"), str(output / "cached-parity.o"),
+         str(splitter_object), *frameworks, "-framework", "ReactNativeShared", "-o", str(parity)])
+    executables = {}
+    for mode in ("native", "cached", "kmp"):
+        executable = output / f"AppleScrollSnapBenchmark-{mode}"
+        run(["xcrun", "clang++", *flags, "-DRCT_SCROLL_BENCHMARK=1", str(harness), str(output / f"{mode}.o"),
+             str(splitter_object), *frameworks, *(["-framework", "ReactNativeShared"] if mode == "kmp" else []),
+             "-Wl,-dead_strip", "-o", str(executable)])
+        executables[mode] = executable
+    mac_sdk = run(["xcrun", "--sdk", "macosx", "--show-sdk-path"]).strip()
+    catalyst = output / "catalyst.o"
+    run(["xcrun", "clang++", "-std=c++20", "-fobjc-arc", "-DRCT_USE_KMP=1", "-DREACT_NATIVE_PRODUCTION",
+         "-target", f"{architecture}-apple-ios15.1-macabi", "-isysroot", mac_sdk,
+         "-isystem", f"{mac_sdk}/System/iOSSupport/usr/include",
+         "-iframework", f"{mac_sdk}/System/iOSSupport/System/Library/Frameworks",
+         "-I", str(output / "include"), "-I", str(react / "ReactCommon"), "-c", str(adapter), "-o", str(catalyst)])
+    if "RNS" in run(["xcrun", "nm", "-u", str(catalyst)]):
+        raise RuntimeError("Catalyst unexpectedly references Kotlin/Native")
+    sources = [adapter, harness, shared / "src/commonMain/kotlin/com/facebook/react/shared/ScrollSnapOffsets.kt"]
+    report = {
+        "configuration": "Release; actual UIKit adapter compiled with KMP enabled and disabled",
+        "platform": f"{architecture} iOS simulator", "sdk": sdk,
+        "cachedNativeControlSha256": hashlib.sha256(cached_path.read_bytes()).hexdigest(),
+        "sourceSha256": {str(path.relative_to(react)): hashlib.sha256(path.read_bytes()).hexdigest() for path in sources},
+        "catalystNativeFallbackCompiled": True, "runtimeExecuted": False,
+        "executableBytes": {mode: path.stat().st_size for mode, path in executables.items()},
+        "benchmarks": [],
+        "limitations": [
+            "Not physical-device performance, gesture interaction, or full-application startup/size.",
+            "First property assignment includes snapshot conversion and lazy Kotlin initialization.",
+            "Repeated flings reuse the property snapshot; each sample includes an autorelease pool per call.",
+            "Cached-native control changes only property storage/access in a staged native adapter copy.",
+            "Runs share the host with unrelated processes; timing is observational, with no pass/fail threshold.",
+            "One unrelated unused Fabric header is omitted; RN logging sanitizer is replaced by a finite-input assertion.",
+        ],
+    }
+    simulator = os.environ.get("RCT_KMP_SIMULATOR_UDID")
+    owned = None
+    try:
+        if not args.build_only:
+            if not simulator:
+                inventory = json.loads(run(["xcrun", "simctl", "list", "-j"]))
+                runtime = next((item for item in inventory["runtimes"]
+                                if item.get("isAvailable") and "iOS" in item["identifier"]), None)
+                device = next((item["identifier"] for item in (runtime or {}).get("supportedDeviceTypes", [])
+                               if "iPhone" in item["name"]), None)
+                if not device:
+                    raise RuntimeError("Install a compatible iOS simulator runtime")
+                owned = run(["xcrun", "simctl", "create", "KMP Scroll Snap Validation", device, runtime["identifier"]]).strip()
+                simulator = owned
+            report["parity"] = json.loads(run(["xcrun", "simctl", "spawn", "--standalone", simulator, str(parity)]))
+            report["runtimeExecuted"] = True
+            for repetition in range(args.benchmark_repeats):
+                for count in (3, 16, 256):
+                    for mode in (("native", "cached", "kmp") if repetition % 2 == 0 else ("kmp", "cached", "native")):
+                        measurement = json.loads(run(["xcrun", "simctl", "spawn", "--standalone", simulator,
+                                                      str(executables[mode]), str(count)]))
+                        measurement.update(mode=mode, repetition=repetition)
+                        report["benchmarks"].append(measurement)
+    finally:
+        if owned:
+            run(["xcrun", "simctl", "delete", owned])
+        (output / "results.json").write_text(json.dumps(report, indent=2) + "\n")
+    print(json.dumps(report, indent=2))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/packages/react-native/ReactShared/scripts/test-apple-smoke.sh b/packages/react-native/ReactShared/scripts/test-apple-smoke.sh
new file mode 100755
index 000000000000..81ed4afe4c4e
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-apple-smoke.sh
@@ -0,0 +1,51 @@
+#!/bin/bash
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+set -euo pipefail
+
+shared_root="$(cd "$(dirname "$0")/.." && pwd)"
+architecture="$(uname -m)"
+case "$architecture" in
+  arm64) target=IosSimulatorArm64; kotlin_target=iosSimulatorArm64 ;;
+  x86_64) target=IosX64; kotlin_target=iosX64 ;;
+  *) echo "error: Unsupported simulator architecture: $architecture" >&2; exit 1 ;;
+esac
+
+"$shared_root/gradlew" -p "$shared_root" -PreactNativeSharedSmoke=true \
+  "linkDebugFramework$target" "linkReleaseFramework$target" --max-workers=2 --console=plain
+
+output="$shared_root/build/smoke/apple-interop"
+mkdir -p "$output"
+sdk="$(xcrun --sdk iphonesimulator --show-sdk-path)"
+simulator="${RCT_KMP_SIMULATOR_UDID:-}"
+if [[ -z "$simulator" ]]; then
+  simulator="$(xcrun simctl list -j | python3 -c '
+import json, sys
+state = json.load(sys.stdin)
+runtimes = sorted((r for r in state["runtimes"] if r.get("isAvailable") and ".iOS-" in r["identifier"]),
+                  key=lambda r: tuple(map(int, r["version"].split("."))), reverse=True)
+for runtime in runtimes:
+    devices = [d for d in state["devices"].get(runtime["identifier"], []) if d.get("isAvailable")]
+    if devices:
+        print(devices[0]["udid"])
+        break
+')"
+fi
+if [[ -z "$simulator" ]]; then
+  echo 'error: Install an iOS simulator runtime and create a device in Xcode.' >&2
+  exit 1
+fi
+
+for configuration in debug release; do
+  frameworks="$shared_root/build/smoke/bin/$kotlin_target/${configuration}Framework"
+  executable="$output/AppleKmpSmoke-$configuration"
+  xcrun clang++ -std=c++20 -fobjc-arc -target "$architecture-apple-ios15.1-simulator" \
+    -isysroot "$sdk" -F "$frameworks" "$shared_root/tests/smoke/AppleKmpSmoke.mm" \
+    -framework ReactNativeShared -framework Foundation -o "$executable"
+  # Standalone execution does not boot or alter the selected simulator.
+  xcrun simctl spawn --standalone "$simulator" "$executable" 2>&1 | tee "$output/$configuration.log"
+  grep -q '^Kotlin Objective-C smoke passed: 5 cases$' "$output/$configuration.log"
+done
diff --git a/packages/react-native/ReactShared/scripts/test-cocoapods-linking.rb b/packages/react-native/ReactShared/scripts/test-cocoapods-linking.rb
new file mode 100644
index 000000000000..a84e91918087
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-cocoapods-linking.rb
@@ -0,0 +1,200 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+require 'cocoapods'
+require 'fileutils'
+require 'json'
+require 'open3'
+require 'tmpdir'
+
+shared_root = File.expand_path('..', __dir__)
+helper = File.expand_path('../scripts/cocoapods/kmp.rb', shared_root)
+output_root = ENV['RCT_KMP_LINKING_TEST_OUTPUT_DIR'] || Dir.mktmpdir('react-native-kmp-linking-')
+FileUtils.mkdir_p(output_root)
+results = []
+
+# These local pods exercise CocoaPods' real dependency and target-inheritance
+# handling without downloading dependencies or compiling a Kotlin framework.
+[nil, 'static', 'dynamic', 'mixed'].each do |linkage|
+  name = linkage || 'static-library'
+  fixture = File.join(output_root, name)
+  FileUtils.mkdir_p(fixture)
+  project = Xcodeproj::Project.new(File.join(fixture, 'Fixture.xcodeproj'))
+  host = project.new_target(:application, 'Host', :ios, '15.1')
+  project.new_target(:application, 'CoreOnly', :ios, '15.1')
+  hosted = project.new_target(:unit_test_bundle, 'HostedTests', :ios, '15.1')
+  sibling = project.new_target(:unit_test_bundle, 'SiblingHostedTests', :ios, '15.1')
+  without_metadata = project.new_target(:unit_test_bundle, 'SiblingWithoutMetadata', :ios, '15.1')
+  standalone = project.new_target(:unit_test_bundle, 'StandaloneTests', :ios, '15.1')
+  plain_host = project.new_target(:application, 'PlainHost', :ios, '15.1')
+  separate = project.new_target(:unit_test_bundle, 'TestsWithNonKMPHost', :ios, '15.1')
+  stale = project.new_target(:unit_test_bundle, 'StaleHostMetadataTests', :ios, '15.1')
+  mismatched = project.new_target(:unit_test_bundle, 'MismatchedLoaderTests', :ios, '15.1')
+  sdk_hosted = project.new_target(:unit_test_bundle, 'SDKHostedTests', :ios, '15.1')
+  unresolved = project.new_target(:unit_test_bundle, 'UnresolvedHostTests', :ios, '15.1')
+  renamed = project.new_target(:application, 'OriginalName', :ios, '15.1')
+  renamed.name = 'Renamed Host'
+  renamed_test = project.new_target(:unit_test_bundle, 'RenamedHostTests', :ios, '15.1')
+
+  # Neither a mere app dependency nor an unrelated KMP app is the test's host.
+  [standalone, separate, stale].each { |test| test.add_dependency(host) }
+  sdk_hosted.add_dependency(plain_host)
+  unresolved.add_dependency(plain_host)
+  [[hosted, host], [sibling, host], [without_metadata, host], [separate, plain_host],
+   [stale, plain_host], [mismatched, host], [renamed_test, renamed], [sdk_hosted, host],
+   [unresolved, host]].each do |test, app|
+    test.add_dependency(app)
+    test.build_configurations.each do |config|
+      config.build_settings['TEST_HOST'] = "$(BUILT_PRODUCTS_DIR)/#{app.name}.app/#{app.name}"
+      config.build_settings['BUNDLE_LOADER'] = '$(TEST_HOST)'
+    end
+  end
+  [hosted, sibling, stale].each do |test|
+    (project.root_object.attributes['TargetAttributes'] ||= {})[test.uuid] = { 'TestTargetID' => host.uuid }
+  end
+  mismatched.build_configurations.each do |config|
+    config.build_settings['BUNDLE_LOADER'] = '$(BUILT_PRODUCTS_DIR)/PlainHost.app/PlainHost'
+  end
+  sdk_hosted.build_configurations.each do |config|
+    config.build_settings['TEST_HOST[sdk=iphonesimulator*]'] = '$(BUILT_PRODUCTS_DIR)/PlainHost.app/PlainHost'
+  end
+  unresolved.build_configurations.each do |config|
+    # An unresolved qualifier must not be overwritten by a later matching SDK key.
+    config.build_settings['TEST_HOST[arch=arm64]'] = '$(BUILT_PRODUCTS_DIR)/PlainHost.app/PlainHost'
+    config.build_settings['TEST_HOST[sdk=iphonesimulator*]'] = '$(BUILT_PRODUCTS_DIR)/Host.app/Host'
+  end
+  renamed.build_configurations.each do |config|
+    product_config = File.join(fixture, "products-#{config.name}.xcconfig")
+    File.write(product_config, <<~XCCONFIG)
+      #include? "Pods/Target Support Files/Pods-Renamed Host/Pods-Renamed Host.#{config.name.downcase}.xcconfig"
+      APP_BUNDLE_BASE = $(PROJECT_NAME) #{config.name}
+    XCCONFIG
+    config.base_configuration_reference = project.new_file(product_config)
+    config.build_settings['PRODUCT_NAME'] = '$(APP_BUNDLE_BASE) Product'
+    config.build_settings['PRODUCT_NAME[sdk=iphonesimulator*]'] = '$(APP_BUNDLE_BASE) Simulator Product'
+    config.build_settings['EXECUTABLE_NAME'] = '$(TARGET_NAME) Binary'
+    test_config = renamed_test.build_configuration_list[config.name]
+    test_config.build_settings['TEST_HOST'] = "\"${BUILT_PRODUCTS_DIR}/Fixture #{config.name} Product.app/$(BUNDLE_EXECUTABLE_FOLDER_PATH)/Renamed Host Binary\""
+    test_config.build_settings['BUNDLE_LOADER'] = "$(BUILT_PRODUCTS_DIR)/Fixture #{config.name} Product.app/Renamed Host Binary"
+    test_config.build_settings['TEST_HOST[sdk=iphonesimulator*]'] = "${BUILT_PRODUCTS_DIR}/Fixture #{config.name} Simulator Product.app/Renamed Host Binary"
+    test_config.build_settings['BUNDLE_LOADER[sdk=iphonesimulator*]'] = '$(TEST_HOST)'
+  end
+  project.save
+
+  %w[React-Core React-RCTFabric TestSupport].each do |pod_name|
+    pod_dir = File.join(fixture, pod_name)
+    FileUtils.mkdir_p(pod_dir)
+    File.write(File.join(pod_dir, 'Fixture.m'), "#import <Foundation/Foundation.h>\n")
+    File.write(File.join(pod_dir, "#{pod_name}.podspec"), <<~PODSPEC)
+      Pod::Spec.new do |s|
+        s.name = #{pod_name.dump}
+        s.version = '1.0.0'
+        s.summary = 'Local CocoaPods linking fixture.'
+        s.homepage = 'https://reactnative.dev/'
+        s.license = { :type => 'MIT', :text => 'Test fixture' }
+        s.author = 'React Native'
+        s.source = { :git => 'https://example.invalid/fixture.git' }
+        s.platform = :ios, '15.1'
+        s.source_files = 'Fixture.m'
+        #{"s.dependency 'React-KMP'" if pod_name == 'React-Core'}
+        #{"s.dependency 'React-Core'" if pod_name == 'React-RCTFabric'}
+      end
+    PODSPEC
+  end
+
+  File.write(File.join(fixture, 'helpers.rb'), <<~HELPERS)
+    require #{helper.dump}
+    def min_supported_versions
+      { :ios => '15.1' }
+    end
+  HELPERS
+  File.write(File.join(fixture, 'Podfile'), <<~PODFILE)
+    require_relative './helpers'
+    platform :ios, '15.1'
+    install! 'cocoapods', :warn_for_unused_master_specs_repo => false
+    project 'Fixture.xcodeproj'
+    #{"use_frameworks! :linkage => :#{linkage}" if linkage && linkage != 'mixed'}
+    target 'Host' do
+      #{"use_frameworks! :linkage => :dynamic" if linkage == 'mixed'}
+      pod 'React-KMP', :path => #{shared_root.dump}
+      pod 'React-Core', :path => './React-Core'
+      pod 'React-RCTFabric', :path => './React-RCTFabric'
+      target 'HostedTests' do
+        inherit! :search_paths
+        pod 'TestSupport', :path => './TestSupport'
+      end
+    end
+    #{['StandaloneTests', 'SiblingHostedTests', 'SiblingWithoutMetadata', 'Renamed Host', 'RenamedHostTests',
+       'TestsWithNonKMPHost', 'StaleHostMetadataTests', 'MismatchedLoaderTests', 'SDKHostedTests', 'UnresolvedHostTests'].map do |target|
+      <<~TARGET
+        target #{target.dump} do
+          #{'use_frameworks! :linkage => :static' if linkage == 'mixed'}
+          pod 'React-KMP', :path => #{shared_root.dump}
+          pod 'React-Core', :path => './React-Core'
+          pod 'React-RCTFabric', :path => './React-RCTFabric'
+        end
+      TARGET
+    end.join}
+    target 'CoreOnly' do
+      #{'use_frameworks! :linkage => :static' if linkage == 'mixed'}
+      pod 'React-KMP', :path => #{shared_root.dump}
+      pod 'React-Core', :path => './React-Core'
+    end
+    target 'PlainHost' do
+      pod 'TestSupport', :path => './TestSupport'
+    end
+    post_install do |installer|
+      installer.aggregate_targets.each do |aggregate|
+        aggregate.xcconfigs.each_key do |configuration|
+          %w[iphoneos iphonesimulator].each do |sdk|
+            target = aggregate.user_targets.first.name
+            expected = %w[HostedTests SiblingHostedTests SiblingWithoutMetadata RenamedHostTests].include?(target) || (target == 'SDKHostedTests' && sdk == 'iphoneos')
+            actual = ReactNativeKMPUtils.test_host_links_kmp?(aggregate, configuration, installer.aggregate_targets, sdk)
+            raise "Wrong KMP host detection for \#{aggregate.label}/\#{configuration}/\#{sdk}: \#{actual}" unless actual == expected
+          end
+        end
+      end
+      ReactNativeKMPUtils.configure_aggregate_xcconfig(installer)
+      ReactNativeKMPUtils.configure_aggregate_xcconfig(installer)
+    end
+  PODFILE
+
+  output, status = Open3.capture2e(
+    { 'COCOAPODS_DISABLE_STATS' => 'true', 'COCOAPODS_NO_BUNDLER' => 'true' },
+    RbConfig.ruby, Gem.bin_path('cocoapods', 'pod'), 'install',
+    "--project-directory=#{fixture}", '--no-repo-update'
+  )
+  File.write(File.join(fixture, 'pod-install.log'), output)
+  raise "CocoaPods #{name} fixture failed: #{output}" unless status.success?
+
+  ['Host', 'HostedTests', 'SiblingHostedTests', 'SiblingWithoutMetadata', 'Renamed Host', 'RenamedHostTests',
+   'CoreOnly', 'StandaloneTests', 'TestsWithNonKMPHost', 'StaleHostMetadataTests', 'MismatchedLoaderTests', 'SDKHostedTests', 'UnresolvedHostTests', 'PlainHost'].each do |target|
+    %w[debug release].each do |configuration|
+      config_path = File.join(fixture, 'Pods', 'Target Support Files', "Pods-#{target}", "Pods-#{target}.#{configuration}.xcconfig")
+      config = Xcodeproj::Config.new(Pathname.new(config_path)).attributes
+      dynamic = linkage == 'dynamic' || (linkage == 'mixed' && target == 'Host')
+      counts = {}
+      %w[iphoneos iphonesimulator].each do |sdk|
+        hosted_kmp = %w[HostedTests SiblingHostedTests SiblingWithoutMetadata RenamedHostTests].include?(target) || (target == 'SDKHostedTests' && sdk == 'iphoneos')
+        expected = target == 'PlainHost' || hosted_kmp || dynamic ? 0 : 1
+        flags = config["OTHER_LDFLAGS[sdk=#{sdk}*]"].to_s
+        count = flags.scan('-framework ReactNativeShared').length
+        raise "#{name}/#{target}/#{configuration}/#{sdk}: expected #{expected} Kotlin links, got #{count}" unless count == expected
+        search_paths = config["FRAMEWORK_SEARCH_PATHS[sdk=#{sdk}*]"].to_s
+        if target != 'PlainHost' && !search_paths.include?('ReactNativeSharedKMP')
+          raise "Missing inherited framework search path for #{name}/#{target}"
+        end
+        counts[sdk] = count
+      end
+      raise "Unconditional Kotlin link leaks into Catalyst for #{name}/#{target}" if config['OTHER_LDFLAGS'].to_s.include?('ReactNativeShared')
+      results << { :linkage => name, :target => target, :configuration => configuration,
+                   :kotlin_links_per_ios_sdk => counts }
+    end
+  end
+end
+
+File.write(File.join(output_root, 'results.json'), JSON.pretty_generate(results) + "\n")
+puts "Passed #{results.length} CocoaPods configurations across static libraries, static frameworks, dynamic frameworks, and mixed per-target linkage."
+puts "Generated fixture configs and logs: #{output_root}"
diff --git a/packages/react-native/ReactShared/scripts/test-kotlin-coexistence.py b/packages/react-native/ReactShared/scripts/test-kotlin-coexistence.py
new file mode 100644
index 000000000000..71e740b20676
--- /dev/null
+++ b/packages/react-native/ReactShared/scripts/test-kotlin-coexistence.py
@@ -0,0 +1,141 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+"""Check two independent Kotlin/Native frameworks built with the same compiler.
+
+Tests all four combinations of static and dynamic runtime ownership. No
+Kotlin classes are cast between frameworks. This does not promise compatibility
+with arbitrary third-party compiler versions or exported Kotlin dependencies.
+"""
+
+import argparse
+import json
+import os
+import pathlib
+import platform
+import re
+import subprocess
+
+
+def run(command, log):
+    result = subprocess.run([str(item) for item in command], capture_output=True, text=True)
+    log.write_text(result.stdout + result.stderr)
+    if result.returncode:
+        raise RuntimeError(f"Command failed with exit {result.returncode}; inspect {log}")
+    return result
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--build-only", action="store_true", help="Compile and inspect linkage without simulator execution.")
+    parser.add_argument("--output", type=pathlib.Path)
+    args = parser.parse_args()
+    shared = pathlib.Path(__file__).resolve().parent.parent
+    output = (args.output or shared / "build/kotlin-coexistence").resolve()
+    output.mkdir(parents=True, exist_ok=True)
+    fixture = shared / "tests/coexistence"
+    version_matches = re.findall(r'kotlin\("multiplatform"\) version "([^"]+)"', (shared / "build.gradle.kts").read_text())
+    if len(version_matches) != 1:
+        raise RuntimeError("Cannot identify the shared module's Kotlin compiler version.")
+    version = version_matches[0]
+    architecture = platform.machine()
+    host = "macos-aarch64" if architecture == "arm64" else "macos-x86_64"
+    target = "ios_simulator_arm64" if architecture == "arm64" else "ios_x64"
+    konan = pathlib.Path(os.environ.get("KONAN_DATA_DIR", pathlib.Path.home() / ".konan"))
+    compiler = pathlib.Path(os.environ.get("RCT_KMP_KONANC", konan / f"kotlin-native-prebuilt-{host}-{version}/bin/konanc"))
+    if not compiler.is_file():
+        raise RuntimeError("Build ReactShared once to install its compiler, or set RCT_KMP_KONANC to the matching konanc.")
+    compiler_version = run([compiler, "-version"], output / "compiler-version.log")
+    if not re.search(rf'(?<![\d.]){re.escape(version)}(?![\d.])', compiler_version.stdout + compiler_version.stderr):
+        raise RuntimeError(f"Coexistence fixture requires the same compiler as ReactShared ({version}).")
+    framework_task = "linkReleaseFrameworkIosSimulatorArm64" if architecture == "arm64" else "linkReleaseFrameworkIosX64"
+    run([shared / "gradlew", "-p", shared, framework_task, "--max-workers=2", "--console=plain"], output / "shared-build.log")
+    kotlin_target = "iosSimulatorArm64" if architecture == "arm64" else "iosX64"
+    shared_frameworks = shared / f"build/bin/{kotlin_target}/releaseFramework"
+    for linkage in ("static", "dynamic"):
+        (output / linkage).mkdir(exist_ok=True)
+        command = [compiler, fixture / "IndependentKotlin.kt", "-target", target, "-produce", "framework", "-opt",
+                   "-Xbinary=bundleId=com.facebook.react.kmp.independentfixture", "-o", output / linkage / "IndependentKotlin"]
+        if linkage == "static":
+            command.append("-Xstatic-framework")
+        run(command, output / f"independent-{linkage}.log")
+    sdk = subprocess.check_output(["xcrun", "--sdk", "iphonesimulator", "--show-sdk-path"], text=True).strip()
+    flags = ["-std=c++20", "-fobjc-arc", "-O2", "-target", f"{architecture}-apple-ios15.1-simulator", "-isysroot", sdk,
+             "-F", str(shared_frameworks), "-F", str(output / "static")]
+    # React-Core must export the shared classes even when only dependent pods
+    # call them. Exercise its linker flags without any algorithm references.
+    empty_owner = output / "libReactNativeRuntimeOnly.dylib"
+    run(["xcrun", "clang++", *flags, "-dynamiclib", "-ObjC", "-framework", "ReactNativeShared",
+         "-framework", "Foundation", "-Wl,-dead_strip", "-o", empty_owner], output / "empty-owner-link.log")
+    empty_symbols = run(["xcrun", "nm", "-gU", empty_owner], output / "empty-owner-symbols.log").stdout
+    for class_name in ("RNSBase", "RNSGradientStops"):
+        if f"_OBJC_CLASS_$_{class_name}" not in empty_symbols:
+            raise RuntimeError(f"An owner without algorithm references did not retain {class_name}.")
+    run(["xcrun", "clang++", *flags, "-c", fixture / "ReactNativeRuntimeOwner.mm", "-o", output / "owner.o"], output / "owner-compile.log")
+    run(["xcrun", "clang++", *flags, "-c", fixture / "AppleKotlinCoexistence.mm", "-o", output / "host.o"], output / "host-compile.log")
+    run(["xcrun", "clang++", *flags, "-dynamiclib", output / "owner.o", "-framework", "ReactNativeShared", "-framework", "Foundation",
+         "-Wl,-install_name,@rpath/libReactNativeRuntimeOwner.dylib", "-o", output / "libReactNativeRuntimeOwner.dylib"], output / "owner-link.log")
+    owner_symbols = run(["xcrun", "nm", "-gU", output / "libReactNativeRuntimeOwner.dylib"], output / "owner-defined-symbols.log").stdout
+    if "_OBJC_CLASS_$_RNSBase" not in owner_symbols:
+        raise RuntimeError("Dynamic RN owner does not contain the shared framework's runtime classes.")
+    records = []
+    for name, independent, dynamic_owner in (
+        ("static-static", "static", False),
+        ("static-dynamic", "dynamic", False),
+        ("dynamic-static", "static", True),
+        ("dynamic-dynamic", "dynamic", True),
+    ):
+        executable = output / f"Coexistence-{name}"
+        link = ["xcrun", "clang++", "-fobjc-arc", "-target", f"{architecture}-apple-ios15.1-simulator", "-isysroot", sdk,
+                output / "host.o", "-F", shared_frameworks, "-F", output / independent,
+                "-framework", "IndependentKotlin", "-framework", "Foundation", "-Wl,-dead_strip", "-o", executable]
+        if dynamic_owner:
+            link.extend(["-L", output, "-lReactNativeRuntimeOwner", f"-Wl,-rpath,{output}"])
+        else:
+            link.extend([output / "owner.o", "-framework", "ReactNativeShared"])
+        if independent == "dynamic":
+            link.append(f"-Wl,-rpath,{output / 'dynamic'}")
+        run(link, output / f"{name}-link.log")
+        imports = run(["xcrun", "otool", "-L", executable], output / f"{name}-dependencies.log").stdout
+        # Inspect an exported Objective-C base class to check which Mach-O image
+        # owns RN's runtime classes. Do not rely on private Kotlin symbol names.
+        symbols = run(["xcrun", "nm", "-gU", executable], output / f"{name}-defined-symbols.log").stdout
+        defines_rn_classes = "_OBJC_CLASS_$_RNSBase" in symbols
+        if defines_rn_classes != (not dynamic_owner):
+            raise RuntimeError(f"Unexpected RN runtime ownership in {name}.")
+        defines_independent_classes = "_OBJC_CLASS_$_IndependentKotlinBase" in symbols
+        if defines_independent_classes != (independent == "static"):
+            raise RuntimeError(f"Unexpected independent runtime ownership in {name}.")
+        if dynamic_owner != ("libReactNativeRuntimeOwner.dylib" in imports):
+            raise RuntimeError(f"Unexpected RN runtime owner dependency in {name}.")
+        if (independent == "dynamic") != ("IndependentKotlin.framework/IndependentKotlin" in imports):
+            raise RuntimeError(f"Unexpected independent runtime linkage in {name}.")
+        records.append({"configuration": name, "compiled": True, "runtimeExecuted": False,
+                        "reactNativeRuntimeOwner": "libReactNativeRuntimeOwner.dylib" if dynamic_owner else "host",
+                        "independentRuntimeOwner": "IndependentKotlin.framework" if independent == "dynamic" else "host"})
+    if not args.build_only:
+        simulator = os.environ.get("RCT_KMP_SIMULATOR_UDID")
+        if not simulator:
+            devices = json.loads(subprocess.check_output(["xcrun", "simctl", "list", "devices", "available", "-j"], text=True))["devices"]
+            simulator = next((items[0]["udid"] for runtime, items in devices.items() if ".iOS-" in runtime and items), None)
+        if not simulator:
+            raise RuntimeError("A compatible iOS simulator runtime is required.")
+        for record in records:
+            name = record["configuration"]
+            result = run(["xcrun", "simctl", "spawn", "--standalone", simulator, output / f"Coexistence-{name}"], output / f"{name}-runtime.log")
+            if re.search(r"Class .* is implemented in both", result.stderr):
+                raise RuntimeError(f"Duplicate Objective-C runtime classes in {name}; inspect the runtime log.")
+            if "Kotlin framework coexistence passed" not in result.stdout:
+                raise RuntimeError(f"Missing coexistence success marker for {name}.")
+            record["runtimeExecuted"] = True
+    report = {"kotlinCompiler": version, "target": target, "configurations": records,
+              "scope": "same compiler; independent modules; primitive values copied across API boundaries"}
+    (output / "results.json").write_text(json.dumps(report, indent=2) + "\n")
+    print(f"Kotlin framework coexistence {'compiled' if args.build_only else 'passed'}: {output / 'results.json'}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/packages/react-native/ReactShared/settings.gradle.kts b/packages/react-native/ReactShared/settings.gradle.kts
new file mode 100644
index 000000000000..4d578820419a
--- /dev/null
+++ b/packages/react-native/ReactShared/settings.gradle.kts
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+pluginManagement {
+  repositories {
+    mavenCentral()
+    gradlePluginPortal()
+  }
+}
+
+dependencyResolutionManagement { repositories { mavenCentral() } }
+
+// A separate build isolates the Native compiler from AGP's built-in Kotlin plugin.
+rootProject.name = "react-native-shared"
diff --git a/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/GradientStops.kt b/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/GradientStops.kt
new file mode 100644
index 000000000000..02036cc584f9
--- /dev/null
+++ b/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/GradientStops.kt
@@ -0,0 +1,208 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared
+
+import kotlin.math.abs
+import kotlin.math.ln
+import kotlin.math.pow
+
+/**
+ * A gradient stop after the platform has converted its position to a fraction of the line length.
+ */
+public data class GradientStopInput(public val position: Double?, public val hasColor: Boolean)
+
+/**
+ * A resolved position and the original input colors to interpolate at that position.
+ *
+ * Equal color indices mean the platform should reuse that input color without interpolation.
+ * Otherwise, [weight] is the contribution of [rightColorIndex], between zero and one. Colors stay
+ * on the platform so that its color space, rounding, and rendering behavior are preserved.
+ */
+public data class ResolvedGradientStop(
+    public val position: Double,
+    public val leftColorIndex: Int,
+    public val rightColorIndex: Int,
+    public val weight: Double,
+)
+
+/** Pure CSS gradient stop position fix-up and transition hint calculations. */
+public object GradientStops {
+  /**
+   * Resolves positions and expands each noncentral transition hint into nine interpolation stops.
+   *
+   * Input follows the parsed CSS gradient contract: endpoints have colors, and a transition hint is
+   * a positioned stop without a color between two color stops. Positions may lie outside zero to
+   * one. An empty input returns an empty result. The input is never modified.
+   *
+   * [epsilon] is the platform's existing absolute tolerance for equal distances. Keeping it
+   * explicit preserves the established Android and Apple behavior near centered and endpoint hints.
+   * [useDoublePrecision] preserves Apple's CGFloat (Double) arithmetic. Android uses Float
+   * arithmetic, including the intermediate logarithm, and converts its positions at this boundary.
+   */
+  public fun resolve(
+      stops: List<GradientStopInput>,
+      epsilon: Double,
+      useDoublePrecision: Boolean = false,
+  ): List<ResolvedGradientStop> {
+    if (stops.isEmpty()) {
+      return emptyList()
+    }
+
+    val math = Arithmetic(useDoublePrecision)
+    val positions = arrayOfNulls<Double>(stops.size)
+    var maxPositionSoFar = math.round(stops[0].position ?: 0.0)
+    var hasNullPositions = false
+
+    // Set default endpoint positions and prevent specified positions from moving backwards.
+    for (i in stops.indices) {
+      val position =
+          stops[i].position?.let(math::round)
+              ?: when (i) {
+                0 -> 0.0
+                stops.lastIndex -> 1.0
+                else -> null
+              }
+      if (position != null) {
+        val fixedPosition = math.max(position, maxPositionSoFar)
+        positions[i] = fixedPosition
+        maxPositionSoFar = fixedPosition
+      } else {
+        hasNullPositions = true
+      }
+    }
+
+    // Evenly distribute each run of unpositioned stops between its own surrounding positions.
+    if (hasNullPositions) {
+      var lastDefinedIndex = 0
+      for (i in 1 until positions.size) {
+        val endPosition = positions[i] ?: continue
+        val startPosition = checkNotNull(positions[lastDefinedIndex])
+        val unpositionedStops = i - lastDefinedIndex - 1
+        if (unpositionedStops > 0) {
+          val increment =
+              math.divide(
+                  math.subtract(endPosition, startPosition),
+                  (unpositionedStops + 1).toDouble(),
+              )
+          for (j in 1..unpositionedStops) {
+            positions[lastDefinedIndex + j] =
+                math.add(startPosition, math.multiply(increment, j.toDouble()))
+          }
+        }
+        lastDefinedIndex = i
+      }
+    }
+
+    val resolved =
+        stops.indices
+            .map { i -> ResolvedGradientStop(checkNotNull(positions[i]), i, i, 0.0) }
+            .toMutableList()
+    var indexOffset = 0
+    for (i in 1 until stops.lastIndex) {
+      if (stops[i].hasColor) {
+        continue
+      }
+
+      val index = i + indexOffset
+      val left = resolved[index - 1]
+      val right = resolved[index + 1]
+      val position = resolved[index].position
+      val leftDistance = math.subtract(position, left.position)
+      val rightDistance = math.subtract(right.position, position)
+      val totalDistance = math.subtract(right.position, left.position)
+
+      if (math.equal(leftDistance, rightDistance, epsilon)) {
+        resolved.removeAt(index)
+        --indexOffset
+        continue
+      }
+      if (math.equal(leftDistance, 0.0, epsilon)) {
+        resolved[index] = right.copy(position = position)
+        continue
+      }
+      if (math.equal(rightDistance, 0.0, epsilon)) {
+        resolved[index] = left.copy(position = position)
+        continue
+      }
+
+      // Use the same nine sample positions as the platform implementations, derived from Blink.
+      val samples = ArrayList<Double>(9)
+      if (leftDistance > rightDistance) {
+        for (y in 0..6) {
+          samples.add(math.sample(left.position, leftDistance, (7f + y) / 13f))
+        }
+        samples.add(math.sample(position, rightDistance, 1f / 3f))
+        samples.add(math.sample(position, rightDistance, 2f / 3f))
+      } else {
+        samples.add(math.sample(left.position, leftDistance, 1f / 3f))
+        samples.add(math.sample(left.position, leftDistance, 2f / 3f))
+        for (y in 0..6) {
+          samples.add(math.sample(position, rightDistance, y / 13f))
+        }
+      }
+
+      val hintRelativeOffset = math.divide(leftDistance, totalDistance)
+      val hintLogarithm = math.log(hintRelativeOffset)
+      val logRatio = ln(0.5) / hintLogarithm
+      val intermediateStops =
+          samples.map { sample ->
+            val pointRelativeOffset =
+                math.divide(math.subtract(sample, left.position), totalDistance)
+            ResolvedGradientStop(
+                sample,
+                left.leftColorIndex,
+                right.rightColorIndex,
+                pointRelativeOffset.pow(logRatio),
+            )
+          }
+      resolved.removeAt(index)
+      resolved.addAll(index, intermediateStops)
+      indexOffset += 8
+    }
+    return resolved
+  }
+
+  /** Keeps every platform operation at its original precision without duplicating the algorithm. */
+  private class Arithmetic(private val doublePrecision: Boolean) {
+    fun round(value: Double): Double = if (doublePrecision) value else value.toFloat().toDouble()
+
+    fun add(first: Double, second: Double): Double =
+        if (doublePrecision) first + second else (first.toFloat() + second.toFloat()).toDouble()
+
+    fun subtract(first: Double, second: Double): Double =
+        if (doublePrecision) first - second else (first.toFloat() - second.toFloat()).toDouble()
+
+    fun multiply(first: Double, second: Double): Double =
+        if (doublePrecision) first * second else (first.toFloat() * second.toFloat()).toDouble()
+
+    fun divide(first: Double, second: Double): Double =
+        if (doublePrecision) first / second else (first.toFloat() / second.toFloat()).toDouble()
+
+    fun max(first: Double, second: Double): Double =
+        if (doublePrecision) {
+          // Match std::max, including its behavior for NaN and signed zero.
+          if (first < second) second else first
+        } else {
+          maxOf(first.toFloat(), second.toFloat()).toDouble()
+        }
+
+    fun log(value: Double): Double =
+        if (doublePrecision) ln(value) else ln(value.toFloat()).toDouble()
+
+    fun equal(first: Double, second: Double, epsilon: Double): Boolean =
+        if (first.isNaN() || second.isNaN()) {
+          first.isNaN() && second.isNaN()
+        } else {
+          abs(subtract(second, first)) < epsilon
+        }
+
+    fun sample(start: Double, distance: Double, fraction: Float): Double =
+        // Both native implementations originally compute these sample fractions as Float.
+        add(start, multiply(distance, fraction.toDouble()))
+  }
+}
diff --git a/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/MultipartFraming.kt b/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/MultipartFraming.kt
new file mode 100644
index 000000000000..70ec180d0390
--- /dev/null
+++ b/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/MultipartFraming.kt
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared
+
+/** A completed region in the caller's current buffer. The first region is the preamble. */
+public class MultipartChunk(
+    public val start: Long,
+    public val end: Long,
+    public val isPart: Boolean,
+    public val isLast: Boolean,
+)
+
+/**
+ * Incremental multipart framing, independent of stream and buffer ownership.
+ *
+ * The caller searches its native buffer for delimiters starting at [searchStart], then passes their
+ * indices to [nextChunk]. After a chunk, it may discard bytes before the delimiter and advance
+ * bufferOffset by the same amount. Offsets let both sliding and retained buffers use the same state
+ * machine without copying body bytes into Kotlin.
+ */
+public class MultipartFraming(
+    private val delimiterLength: Int,
+    private val closeDelimiterLength: Int,
+) {
+  private var chunkStart: Long = 0
+  private var bytesSeen: Long = 0
+  private var hasBoundary: Boolean = false
+
+  /** Retain enough overlap to find a delimiter split between two reads. */
+  public fun searchStart(bufferOffset: Long): Long =
+      maxOf(bytesSeen - closeDelimiterLength, chunkStart) - bufferOffset
+
+  /** Start of the current part in the caller's buffer, including its headers. */
+  public fun partStart(bufferOffset: Long): Long = chunkStart - bufferOffset
+
+  /**
+   * Returns a completed region, or null when another read is needed. A negative index means that
+   * delimiter was not found. Normal delimiters take precedence, matching both adapters.
+   */
+  public fun nextChunk(
+      bufferLength: Long,
+      bufferOffset: Long,
+      delimiterIndex: Long,
+      closeDelimiterIndex: Long,
+  ): MultipartChunk? {
+    val isClosing = delimiterIndex < 0
+    val end = if (isClosing) closeDelimiterIndex else delimiterIndex
+    if (end < 0) {
+      bytesSeen = bufferOffset + bufferLength
+      return null
+    }
+
+    val chunk = MultipartChunk(chunkStart - bufferOffset, end, hasBoundary, isClosing)
+    if (!isClosing) {
+      hasBoundary = true
+      chunkStart = bufferOffset + end + delimiterLength
+      bytesSeen = chunkStart
+    }
+    return chunk
+  }
+}
+
+/** An untrimmed header. Native adapters retain their whitespace and map-key policies. */
+public class MultipartHeader(public val name: String, public val value: String)
+
+public object MultipartHeaders {
+  /** Split CRLF-delimited headers at the first colon, ignoring lines without a separator. */
+  public fun parse(text: String): List<MultipartHeader> =
+      text.split("\r\n").mapNotNull { line ->
+        val separator = line.indexOf(':')
+        if (separator < 0) null
+        else MultipartHeader(line.substring(0, separator), line.substring(separator + 1))
+      }
+}
diff --git a/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/ScrollSnapOffsets.kt b/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/ScrollSnapOffsets.kt
new file mode 100644
index 000000000000..753232d99f3d
--- /dev/null
+++ b/packages/react-native/ReactShared/src/commonMain/kotlin/com/facebook/react/shared/ScrollSnapOffsets.kt
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared
+
+import kotlin.math.abs
+
+/** Why a fling selected an offset; platforms retain their own velocity adjustments. */
+public enum class ScrollSnapDirection {
+  NONE,
+  FORWARD,
+  BACKWARD,
+}
+
+/** The bounded target and the original snap point used by native fling physics. */
+public class ScrollSnapResult
+internal constructor(
+    public val targetOffset: Double,
+    public val selectedOffset: Double,
+    public val direction: ScrollSnapDirection,
+)
+
+/**
+ * Selects explicit scroll snap offsets in platform-resolved coordinates.
+ *
+ * The DoubleArray constructor copies its input for an Apple property snapshot. Android uses
+ * [fromIntegerOffsets] to retain its existing native list and 32-bit pixel arithmetic. Inputs are
+ * never sorted: the first and last elements define free-scrolling boundaries. Callers retain
+ * density conversion, RTL coordinates, target prediction and interval snapping.
+ */
+public class ScrollSnapOffsets
+private constructor(
+    private val fractionalOffsets: DoubleArray?,
+    private val integerOffsets: List<Int>?,
+) {
+  public constructor(offsets: DoubleArray) : this(offsets.copyOf(), null)
+
+  public companion object {
+    /**
+     * Retains the caller's list so native mutations remain visible on the next fling. The list must
+     * be nonempty when resolving; platforms keep their existing empty-list fallback policy.
+     */
+    public fun fromIntegerOffsets(offsets: List<Int>): ScrollSnapOffsets =
+        ScrollSnapOffsets(null, offsets)
+  }
+
+  private fun offsetAt(index: Int): Double =
+      if (integerOffsets != null) integerOffsets[index].toDouble()
+      else checkNotNull(fractionalOffsets)[index]
+
+  private fun distance(left: Double, right: Double): Double =
+      if (integerOffsets != null) (left.toInt() - right.toInt()).toDouble() else left - right
+
+  /**
+   * Coordinates must be finite and [maximumOffset] nonnegative. An empty DoubleArray leaves the
+   * predicted target unchanged apart from bounding it. A midpoint tie selects the larger offset.
+   * [ScrollSnapResult.selectedOffset] precedes bounding for Android's native velocity adjustment.
+   */
+  public fun resolve(
+      currentOffset: Double,
+      targetOffset: Double,
+      maximumOffset: Double,
+      velocity: Double,
+      snapToStart: Boolean,
+      snapToEnd: Boolean,
+  ): ScrollSnapResult {
+    val count = integerOffsets?.size ?: checkNotNull(fractionalOffsets).size
+    if (integerOffsets == null && count == 0) {
+      return ScrollSnapResult(
+          targetOffset.coerceIn(0.0, maximumOffset),
+          targetOffset,
+          ScrollSnapDirection.NONE,
+      )
+    }
+    val firstOffset = offsetAt(0)
+    val lastOffset = offsetAt(count - 1)
+    var smallerOffset = 0.0
+    var largerOffset = maximumOffset
+    for (i in 0 until count) {
+      val offset = offsetAt(i)
+      if (
+          offset <= targetOffset &&
+              distance(targetOffset, offset) < distance(targetOffset, smallerOffset)
+      ) {
+        smallerOffset = offset
+      }
+      if (
+          offset >= targetOffset &&
+              distance(offset, targetOffset) < distance(largerOffset, targetOffset)
+      ) {
+        largerOffset = offset
+      }
+    }
+
+    var selectedOffset = targetOffset
+    var direction = ScrollSnapDirection.NONE
+    if (!snapToEnd && targetOffset >= lastOffset) {
+      if (currentOffset < lastOffset) {
+        selectedOffset = lastOffset
+      }
+    } else if (!snapToStart && targetOffset <= firstOffset) {
+      if (currentOffset > firstOffset) {
+        selectedOffset = firstOffset
+      }
+    } else if (velocity > 0) {
+      selectedOffset = largerOffset
+      direction = ScrollSnapDirection.FORWARD
+    } else if (velocity < 0) {
+      selectedOffset = smallerOffset
+      direction = ScrollSnapDirection.BACKWARD
+    } else {
+      val preferSmaller =
+          if (integerOffsets != null) {
+            abs(targetOffset.toInt() - smallerOffset.toInt()) <
+                abs(largerOffset.toInt() - targetOffset.toInt())
+          } else {
+            targetOffset - smallerOffset < largerOffset - targetOffset
+          }
+      selectedOffset = if (preferSmaller) smallerOffset else largerOffset
+    }
+    return ScrollSnapResult(
+        targetOffset = selectedOffset.coerceIn(0.0, maximumOffset),
+        selectedOffset = selectedOffset,
+        direction = direction,
+    )
+  }
+}
diff --git a/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/GradientStopsTest.kt b/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/GradientStopsTest.kt
new file mode 100644
index 000000000000..e8b89637630f
--- /dev/null
+++ b/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/GradientStopsTest.kt
@@ -0,0 +1,262 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared
+
+import kotlin.math.sqrt
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class GradientStopsTest {
+  @Test
+  fun emptyGradientHasNoStops() {
+    assertEquals(emptyList(), GradientStops.resolve(emptyList(), ANDROID_EPSILON))
+  }
+
+  @Test
+  fun singleColorDefaultsToStart() {
+    assertEquals(listOf(original(0f, 0)), resolve(colors(null)))
+  }
+
+  @Test
+  fun positionedColorsKeepTheirInputReferences() {
+    assertEquals(
+        listOf(original(0f, 0), original(.42f, 1)),
+        resolve(colors(0f, .42f)),
+    )
+  }
+
+  @Test
+  fun missingEndpointsDefaultToZeroAndOne() {
+    assertEquals(
+        listOf(original(0f, 0), original(.3f, 1), original(1f, 2)),
+        resolve(colors(null, .3f, null)),
+    )
+  }
+
+  @Test
+  fun allUnpositionedColorsAreEvenlySpaced() {
+    assertEquals(
+        listOf(original(0f, 0), original(1f / 3f, 1), original(2f / 3f, 2), original(1f, 3)),
+        resolve(colors(null, null, null, null)),
+    )
+  }
+
+  @Test
+  fun decreasingPositionsUseTheLargestPreviousPosition() {
+    assertEquals(
+        listOf(0f, .3f, .3f, .6f, .6f),
+        resolve(colors(null, .3f, .2f, .6f, .5f)).map { it.position.toFloat() },
+    )
+  }
+
+  @Test
+  fun positionsOutsideTheGradientArePreserved() {
+    assertEquals(
+        listOf(-1f, 0f, 1f, 2f),
+        resolve(colors(-1f, null, 1f, 2f)).map { it.position.toFloat() },
+    )
+    assertEquals(listOf(2f, 2f), resolve(colors(2f, null)).map { it.position.toFloat() })
+  }
+
+  @Test
+  fun eachUnpositionedRunUsesItsOwnAdjacentStops() {
+    assertEquals(
+        listOf(0f, .2f, .5f, .8f, .9f, 1f),
+        resolve(colors(0f, .2f, null, .8f, null, 1f)).map { it.position.toFloat() },
+    )
+  }
+
+  @Test
+  fun centeredHintDoesNotAddAnInterpolationStop() {
+    assertEquals(
+        listOf(original(0f, 0), original(1f, 2)),
+        resolve(listOf(color(0f), hint(.5f), color(1f))),
+    )
+  }
+
+  @Test
+  fun hintInCollapsedIntervalIsRemovedBeforeEndpointReplacement() {
+    assertEquals(
+        listOf(original(.3f, 0), original(.3f, 2)),
+        resolve(listOf(color(.3f), hint(.2f), color(.1f))),
+    )
+  }
+
+  @Test
+  fun hintAtLeftEndpointReusesRightColor() {
+    assertEquals(
+        listOf(original(0f, 0), original(0f, 2), original(1f, 2)),
+        resolve(listOf(color(0f), hint(0f), color(1f))),
+    )
+  }
+
+  @Test
+  fun hintAtRightEndpointReusesLeftColor() {
+    assertEquals(
+        listOf(original(0f, 0), original(1f, 0), original(1f, 2)),
+        resolve(listOf(color(0f), hint(1f), color(1f))),
+    )
+  }
+
+  @Test
+  fun platformTolerancePreservesNearCenteredHintBehavior() {
+    val inputs = listOf(color(0f), hint(.502f), color(1f))
+    assertEquals(11, resolve(inputs).size)
+    assertEquals(2, GradientStops.resolve(inputs, APPLE_EPSILON).size)
+  }
+
+  @Test
+  fun platformTolerancePreservesNearEndpointHintBehavior() {
+    val inputs = listOf(color(0f), hint(.002f), color(1f))
+    assertEquals(11, resolve(inputs).size)
+    assertEquals(
+        listOf(original(0f, 0), original(.002f, 2), original(1f, 2)),
+        GradientStops.resolve(inputs, APPLE_EPSILON),
+    )
+  }
+
+  @Test
+  fun leftHintUsesNineSamplesAndTheExpectedPowerCurve() {
+    val resolved = resolve(listOf(color(0f), hint(.25f), color(1f)))
+    assertEquals(11, resolved.size)
+    assertEquals(original(0f, 0), resolved.first())
+    assertEquals(original(1f, 2), resolved.last())
+    val samples = resolved.subList(1, 10)
+    val expectedPositions =
+        listOf(
+            .083333336f,
+            .16666667f,
+            .25f,
+            .30769232f,
+            .36538464f,
+            .42307693f,
+            .48076925f,
+            .53846157f,
+            .59615386f,
+        )
+    assertEquals(expectedPositions, samples.map { it.position.toFloat() })
+    for (sample in samples) {
+      assertEquals(0, sample.leftColorIndex)
+      assertEquals(2, sample.rightColorIndex)
+      // A quarter-position hint has exponent 1/2; Float logarithm rounding is retained.
+      assertEquals(sqrt(sample.position.toDouble()), sample.weight, absoluteTolerance = 1e-7)
+    }
+  }
+
+  @Test
+  fun rightHintUsesNineSamplesAndEqualMixAtTheHint() {
+    val resolved = resolve(listOf(color(0f), hint(.75f), color(1f)))
+    val samples = resolved.subList(1, 10)
+    assertEquals(
+        listOf(
+            .40384617f,
+            .4615385f,
+            .5192308f,
+            .5769231f,
+            .6346154f,
+            .6923077f,
+            .75f,
+            .8333333f,
+            .9166667f,
+        ),
+        samples.map { it.position.toFloat() },
+    )
+    assertEquals(.5, samples[6].weight, absoluteTolerance = 1e-7)
+    assertTrue(samples.all { it.leftColorIndex == 0 && it.rightColorIndex == 2 })
+    assertTrue(samples.all { it.weight.isFinite() && it.weight in 0.0..1.0 })
+    assertTrue(samples.zipWithNext().all { (left, right) -> left.weight < right.weight })
+  }
+
+  @Test
+  fun appleLogarithmKeepsDoublePrecision() {
+    val inputs = listOf(color(0f), hint(.25f), color(1f))
+    val apple = GradientStops.resolve(inputs, APPLE_EPSILON, useDoublePrecision = true)
+    val android = resolve(inputs)
+
+    assertEquals(.5, apple[3].weight)
+    assertTrue(android[3].weight != apple[3].weight)
+    for (sample in apple.subList(1, 10)) {
+      assertEquals(sqrt(sample.position.toDouble()), sample.weight, absoluteTolerance = 1e-15)
+    }
+  }
+
+  @Test
+  fun appleUnpositionedStopsKeepDoublePrecision() {
+    val inputs = colors(null, null, null, null)
+    val apple = GradientStops.resolve(inputs, APPLE_EPSILON, useDoublePrecision = true)
+
+    assertEquals(listOf(0.0, 1.0 / 3.0, 2.0 / 3.0, 1.0), apple.map { it.position })
+    assertTrue(apple[1].position != resolve(inputs)[1].position)
+  }
+
+  @Test
+  fun applePointDivisionDoesNotRoundAcrossTheCenteredHintThreshold() {
+    // Native point positions use CGFloat division: 100.5 points / 200 points.
+    // Rounding that position to Float changes whether the hint falls inside Apple's tolerance.
+    val inputs =
+        listOf(
+            GradientStopInput(0.0, true),
+            GradientStopInput(100.5 / 200.0, false),
+            GradientStopInput(1.0, true),
+        )
+
+    assertEquals(11, GradientStops.resolve(inputs, APPLE_EPSILON, useDoublePrecision = true).size)
+    assertEquals(2, GradientStops.resolve(inputs, APPLE_EPSILON).size)
+  }
+
+  @Test
+  fun appleSamplesRetainDoublePositionsWithNativeFloatFractions() {
+    val inputs = listOf(color(0f), hint(.25f), color(1f))
+    val apple = GradientStops.resolve(inputs, APPLE_EPSILON, useDoublePrecision = true)
+
+    assertEquals(.25 * (1f / 3f).toDouble(), apple[1].position)
+    assertEquals(.25 + .75 * (6f / 13f).toDouble(), apple[9].position)
+    assertTrue(apple[9].position != resolve(inputs)[9].position)
+  }
+
+  @Test
+  fun multipleHintsReferenceOriginalColorsAfterInsertionsAndRemoval() {
+    val inputs =
+        listOf(color(0f), hint(.1f), color(.5f), hint(.6f), color(.7f), hint(.9f), color(1f))
+    val resolved = resolve(inputs)
+    assertEquals(22, resolved.size)
+    assertEquals(original(.5f, 2), resolved[10])
+    assertEquals(original(.7f, 4), resolved[11])
+    assertEquals(original(1f, 6), resolved[21])
+    assertTrue(resolved.subList(1, 10).all { it.leftColorIndex == 0 && it.rightColorIndex == 2 })
+    assertTrue(resolved.subList(12, 21).all { it.leftColorIndex == 4 && it.rightColorIndex == 6 })
+  }
+
+  @Test
+  fun repeatedResolutionDoesNotChangeTheInputs() {
+    val inputs = listOf(color(null), hint(.2f), color(null), color(.8f), color(null))
+    val snapshot = inputs.toList()
+    assertEquals(resolve(inputs), resolve(inputs))
+    assertEquals(snapshot, inputs)
+  }
+
+  private fun resolve(stops: List<GradientStopInput>): List<ResolvedGradientStop> =
+      GradientStops.resolve(stops, ANDROID_EPSILON)
+
+  private fun colors(vararg positions: Float?): List<GradientStopInput> = positions.map(::color)
+
+  private fun color(position: Float?): GradientStopInput =
+      GradientStopInput(position?.toDouble(), true)
+
+  private fun hint(position: Float): GradientStopInput =
+      GradientStopInput(position.toDouble(), false)
+
+  private fun original(position: Float, colorIndex: Int): ResolvedGradientStop =
+      ResolvedGradientStop(position.toDouble(), colorIndex, colorIndex, 0.0)
+
+  private companion object {
+    val ANDROID_EPSILON = .00001f.toDouble()
+    val APPLE_EPSILON = .005f.toDouble()
+  }
+}
diff --git a/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/MultipartFramingTest.kt b/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/MultipartFramingTest.kt
new file mode 100644
index 000000000000..9e67686648de
--- /dev/null
+++ b/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/MultipartFramingTest.kt
@@ -0,0 +1,139 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+class MultipartFramingTest {
+  @Test
+  fun framingIsIndependentOfReadBoundariesAndBufferRetention() {
+    val input =
+        "preamble\r\n--sample\r\nA: b\r\n\r\none\r\n--sample\r\ntwo\r\n--sample--\r\nepilogue"
+    for (readSize in 1..input.length) {
+      for (discard in listOf(false, true)) {
+        assertEquals(
+            listOf("A: b\r\n\r\none", "two") to true,
+            parse(input, "sample", readSize, discard),
+            "readSize=$readSize discard=$discard",
+        )
+      }
+    }
+  }
+
+  @Test
+  fun missingDelimiterDoesNotComplete() {
+    assertEquals(emptyList<String>() to false, parse("no delimiter", "sample", 1, true))
+  }
+
+  @Test
+  fun missingClosingDelimiterDoesNotComplete() {
+    assertEquals(emptyList<String>() to false, parse("\r\n--sample\r\nbody", "sample", 1, false))
+  }
+
+  @Test
+  fun incompleteFinalPartKeepsPreviouslyCompletedParts() {
+    val input = "\r\n--s\r\nfirst\r\n--s\r\nincomplete"
+    assertEquals(listOf("first") to false, parse(input, "s", 2, true))
+  }
+
+  @Test
+  fun closingDelimiterWithoutPartsOnlyDiscardsPreamble() {
+    assertEquals(emptyList<String>() to true, parse("preamble\r\n--s--\r\n", "s", 1, false))
+  }
+
+  @Test
+  fun nearMatchesRemainInTheBody() {
+    val body = "binary\u0000\r\n--samplX\r\n\r\n--sample-\r\n"
+    val input = "\r\n--sample\r\n$body\r\n--sample--\r\n"
+    for (readSize in 1..input.length) {
+      assertEquals(listOf(body) to true, parse(input, "sample", readSize, true))
+    }
+  }
+
+  @Test
+  fun overlapStartsAtThePartUntilMoreBytesArrive() {
+    val framing = MultipartFraming(7, 9)
+    assertEquals(0L, framing.searchStart(0))
+    val preamble = framing.nextChunk(7, 0, 0, -1)!!
+    assertFalse(preamble.isPart)
+    assertEquals(7L, framing.partStart(0))
+    assertEquals(7L, framing.searchStart(0))
+    assertNull(framing.nextChunk(30, 0, -1, -1))
+    assertEquals(21L, framing.searchStart(0))
+  }
+
+  @Test
+  fun offsetsRemainExactBeyondIntRange() {
+    val framing = MultipartFraming(7, 9)
+    val offset = Int.MAX_VALUE.toLong() + 100
+    framing.nextChunk(offset + 7, 0, offset, -1)
+    assertEquals(7L, framing.partStart(offset))
+    assertNull(framing.nextChunk(30, offset, -1, -1))
+    assertEquals(21L, framing.searchStart(offset))
+    val part = framing.nextChunk(40, offset, -1, 31)!!
+    assertEquals(7L, part.start)
+    assertEquals(31L, part.end)
+    assertTrue(part.isPart)
+    assertTrue(part.isLast)
+  }
+
+  @Test
+  fun normalDelimiterRetainsExistingSearchPrecedence() {
+    val framing = MultipartFraming(7, 9)
+    assertFalse(framing.nextChunk(40, 0, 20, 5)!!.isLast)
+  }
+
+  @Test
+  fun headersRetainNativeWhitespaceCaseAndDuplicatePolicies() {
+    val headers =
+        MultipartHeaders.parse(
+            " Content-Type : text/plain:extra \r\ninvalid\r\nx:1\r\nX:2\r\n:empty\r\n"
+        )
+    assertEquals(listOf(" Content-Type ", "x", "X", ""), headers.map { it.name })
+    assertEquals(listOf(" text/plain:extra ", "1", "2", "empty"), headers.map { it.value })
+    assertTrue(MultipartHeaders.parse("").isEmpty())
+  }
+
+  private fun parse(
+      input: String,
+      boundary: String,
+      readSize: Int,
+      discard: Boolean,
+  ): Pair<List<String>, Boolean> {
+    val delimiter = "\r\n--$boundary\r\n"
+    val closeDelimiter = "\r\n--$boundary--\r\n"
+    val framing = MultipartFraming(delimiter.length, closeDelimiter.length)
+    var buffer = ""
+    var offset = 0L
+    var read = 0
+    val parts = mutableListOf<String>()
+    while (true) {
+      val start = framing.searchStart(offset).toInt()
+      val normal = buffer.indexOf(delimiter, start)
+      val close = if (normal < 0) buffer.indexOf(closeDelimiter, start) else -1
+      val chunk = framing.nextChunk(buffer.length.toLong(), offset, normal.toLong(), close.toLong())
+      if (chunk == null) {
+        if (read == input.length) return parts to false
+        val end = minOf(input.length, read + readSize)
+        buffer += input.substring(read, end)
+        read = end
+      } else {
+        if (chunk.isPart) parts += buffer.substring(chunk.start.toInt(), chunk.end.toInt())
+        if (chunk.isLast) return parts to true
+        if (discard) {
+          buffer = buffer.substring(chunk.end.toInt())
+          offset += chunk.end
+        }
+      }
+    }
+  }
+}
diff --git a/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/ScrollSnapOffsetsTest.kt b/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/ScrollSnapOffsetsTest.kt
new file mode 100644
index 000000000000..e8b75c435a89
--- /dev/null
+++ b/packages/react-native/ReactShared/src/commonTest/kotlin/com/facebook/react/shared/ScrollSnapOffsetsTest.kt
@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class ScrollSnapOffsetsTest {
+  private val offsets = ScrollSnapOffsets(doubleArrayOf(20.0, 60.0, 100.0))
+
+  @Test
+  fun directionAndMidpointTies() {
+    assertEquals(20.0, offsets.resolve(20.0, 39.0, 120.0, 0.0, true, true).targetOffset)
+    assertEquals(60.0, offsets.resolve(20.0, 40.0, 120.0, 0.0, true, true).targetOffset)
+    val forward = offsets.resolve(20.0, 21.0, 120.0, 0.01, true, true)
+    assertEquals(60.0, forward.targetOffset)
+    assertEquals(ScrollSnapDirection.FORWARD, forward.direction)
+    val backward = offsets.resolve(100.0, 99.0, 120.0, -0.01, true, true)
+    assertEquals(60.0, backward.targetOffset)
+    assertEquals(ScrollSnapDirection.BACKWARD, backward.direction)
+    assertEquals(60.0, offsets.resolve(20.0, 60.0, 120.0, 1.0, true, true).targetOffset)
+  }
+
+  @Test
+  fun disabledBoundariesAllowFreeScrollingOnlyAfterCrossing() {
+    assertEquals(20.0, offsets.resolve(30.0, 10.0, 120.0, -1.0, false, false).targetOffset)
+    val freeStart = offsets.resolve(20.0, 10.0, 120.0, -1.0, false, false)
+    assertEquals(10.0, freeStart.targetOffset)
+    assertEquals(ScrollSnapDirection.NONE, freeStart.direction)
+    assertEquals(100.0, offsets.resolve(90.0, 110.0, 120.0, 1.0, false, false).targetOffset)
+    val freeEnd = offsets.resolve(100.0, 110.0, 120.0, 1.0, false, false)
+    assertEquals(110.0, freeEnd.targetOffset)
+    assertEquals(ScrollSnapDirection.NONE, freeEnd.direction)
+  }
+
+  @Test
+  fun boundingDoesNotChangeThePointUsedForVelocityAdjustment() {
+    val result =
+        ScrollSnapOffsets(doubleArrayOf(20.0, 140.0)).resolve(0.0, 150.0, 120.0, -1.0, true, true)
+    assertEquals(120.0, result.targetOffset)
+    assertEquals(140.0, result.selectedOffset)
+    assertEquals(ScrollSnapDirection.BACKWARD, result.direction)
+    assertEquals(0.0, offsets.resolve(0.0, -50.0, 0.0, 0.0, true, true).targetOffset)
+  }
+
+  @Test
+  fun fractionalDuplicateAndEmptyOffsets() {
+    val fractional = ScrollSnapOffsets(doubleArrayOf(0.25, 0.25, 1.75))
+    assertEquals(1.75, fractional.resolve(0.0, 1.0, 2.0, 0.0, true, true).targetOffset)
+    assertEquals(0.25, fractional.resolve(0.0, 0.25, 2.0, -1.0, true, true).targetOffset)
+    assertEquals(
+        1.0,
+        ScrollSnapOffsets(doubleArrayOf()).resolve(0.0, 1.0, 2.0, 1.0, true, true).targetOffset,
+    )
+  }
+
+  @Test
+  fun propertySnapshotPreservesOrderAndIgnoresLaterInputMutation() {
+    val input = doubleArrayOf(100.0, 20.0, 60.0)
+    val snapshot = ScrollSnapOffsets(input)
+    input[0] = 0.0
+    // The first property value is 100, not the sorted minimum of 20.
+    assertEquals(100.0, snapshot.resolve(110.0, 50.0, 120.0, 0.0, false, true).targetOffset)
+    assertEquals(60.0, snapshot.resolve(0.0, 50.0, 120.0, 0.0, true, true).targetOffset)
+  }
+
+  @Test
+  fun integerListsRetainNativeMutationsAndWrappingArithmetic() {
+    val input = mutableListOf(20, 60, 100)
+    val retained = ScrollSnapOffsets.fromIntegerOffsets(input)
+    input[1] = 90
+    assertEquals(90.0, retained.resolve(0.0, 40.0, 300.0, 1.0, true, true).targetOffset)
+    input.add(50)
+    assertEquals(50.0, retained.resolve(0.0, 40.0, 300.0, 1.0, true, true).targetOffset)
+    val extreme = ScrollSnapOffsets.fromIntegerOffsets(listOf(Int.MIN_VALUE, 20, 100))
+    assertEquals(300.0, extreme.resolve(0.0, 150.0, 300.0, 0.0, true, true).targetOffset)
+  }
+}
diff --git a/packages/react-native/ReactShared/tests/AndroidMultipartBenchmark.kt b/packages/react-native/ReactShared/tests/AndroidMultipartBenchmark.kt
new file mode 100644
index 000000000000..3c2f64003645
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/AndroidMultipartBenchmark.kt
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.devsupport
+
+import java.lang.management.ManagementFactory
+import okio.Buffer
+import okio.BufferedSource
+import okio.ByteString
+import okio.ByteString.Companion.toByteString
+
+// Compiled with the actual adapter and the explicitly selected, renamed Git baseline.
+private fun read(native: Boolean, source: BufferedSource, capture: Boolean): Any {
+  var bytes = 0L
+  var calls = 0
+  var result: ByteString? = null
+  fun complete(body: BufferedSource, last: Boolean) {
+    check(last)
+    calls++
+    if (capture) {
+      result = body.readByteString()
+    } else {
+      val scratch = Buffer()
+      while (body.read(scratch, 8192) != -1L) {
+        bytes += scratch.size
+        scratch.clear()
+      }
+    }
+  }
+  val success =
+      if (native) {
+        MultipartStreamReaderBaseline(source, "sample")
+            .readAllParts(
+                object : MultipartStreamReaderBaseline.ChunkListener {
+                  override fun onChunkComplete(
+                      headers: Map<String, String>,
+                      body: BufferedSource,
+                      isLastChunk: Boolean,
+                  ) = complete(body, isLastChunk)
+
+                  override fun onChunkProgress(
+                      headers: Map<String, String>,
+                      loaded: Long,
+                      total: Long,
+                  ) = Unit
+                }
+            )
+      } else {
+        MultipartStreamReader(source, "sample")
+            .readAllParts(
+                object : MultipartStreamReader.ChunkListener {
+                  override fun onChunkComplete(
+                      headers: Map<String, String>,
+                      body: BufferedSource,
+                      isLastChunk: Boolean,
+                  ) = complete(body, isLastChunk)
+
+                  override fun onChunkProgress(
+                      headers: Map<String, String>,
+                      loaded: Long,
+                      total: Long,
+                  ) = Unit
+                }
+            )
+      }
+  check(success && calls == 1)
+  return result ?: bytes
+}
+
+fun main() {
+  val bean = ManagementFactory.getThreadMXBean() as com.sun.management.ThreadMXBean
+  check(bean.isThreadAllocatedMemorySupported)
+  bean.isThreadAllocatedMemoryEnabled = true
+  val thread = Thread.currentThread().id
+  for (megabytes in listOf(2, 20)) {
+    val size = megabytes * 1024 * 1024
+    val body = ByteArray(size) { (it % 251).toByte() }
+    val response =
+        Buffer()
+            .apply {
+              writeUtf8("preamble\r\n--sample\r\nContent-Length: $size\r\n\r\n")
+              write(body)
+              writeUtf8("\r\n--sample--\r\nepilogue")
+            }
+            .readByteArray()
+    val nativeBody = read(true, Buffer().write(response), true)
+    val sharedBody = read(false, Buffer().write(response), true)
+    check(nativeBody == sharedBody && sharedBody == body.toByteString())
+
+    fun measure(native: Boolean): Pair<Double, Long> {
+      val source = Buffer().write(response)
+      val allocated = bean.getThreadAllocatedBytes(thread)
+      val start = System.nanoTime()
+      val result = read(native, source, false)
+      val elapsed = (System.nanoTime() - start) / 1_000_000.0
+      val bytes = bean.getThreadAllocatedBytes(thread) - allocated
+      check(result == size.toLong())
+      return elapsed to bytes
+    }
+    repeat(30) {
+      measure(true)
+      measure(false)
+    }
+    val native = mutableListOf<Pair<Double, Long>>()
+    val shared = mutableListOf<Pair<Double, Long>>()
+    repeat(41) { i ->
+      if (i % 2 == 0) {
+        native += measure(true)
+        shared += measure(false)
+      } else {
+        shared += measure(false)
+        native += measure(true)
+      }
+    }
+    val baselineMs = native.map { it.first }.sorted()[20]
+    val sharedMs = shared.map { it.first }.sorted()[20]
+    println(
+        """{"bytes":$size,"iterations":41,"nativeMedianMs":$baselineMs,"kmpMedianMs":$sharedMs,"ratio":${sharedMs / baselineMs},"nativeMedianAllocatedBytes":${native.map { it.second }.sorted()[20]},"kmpMedianAllocatedBytes":${shared.map { it.second }.sorted()[20]},"nativeSamplesMs":${native.map { it.first }},"kmpSamplesMs":${shared.map { it.first }}}"""
+    )
+  }
+}
diff --git a/packages/react-native/ReactShared/tests/AppleGradientBenchmark.mm b/packages/react-native/ReactShared/tests/AppleGradientBenchmark.mm
new file mode 100644
index 000000000000..ae51335288f3
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/AppleGradientBenchmark.mm
@@ -0,0 +1,154 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <React/RCTGradientUtils.h>
+#import <mach/mach.h>
+#import <react/renderer/graphics/RCTPlatformColorUtils.h>
+
+#include <chrono>
+#include <cstdio>
+#include <cstdlib>
+#include <string>
+
+using namespace facebook::react;
+using Clock = std::chrono::steady_clock;
+
+#if !RCT_BENCHMARK_KMP
+@interface RCTGradientUtilsBaseline : NSObject
++ (std::vector<ProcessedColorStop>)getFixedColorStops:(const std::vector<ColorStop> &)colorStops
+                                   gradientLineLength:(CGFloat)gradientLineLength;
+@end
+#endif
+
+static volatile double checksum = 0;
+
+static void calculate(const std::vector<ColorStop> &input)
+{
+#if RCT_BENCHMARK_KMP
+  auto result = [RCTGradientUtils getFixedColorStops:input gradientLineLength:240];
+#else
+  auto result = [RCTGradientUtilsBaseline getFixedColorStops:input gradientLineLength:240];
+#endif
+  // Observe the output without timing another traversal or color conversion.
+  checksum = checksum + result.size() + result.front().position.value() + result.back().position.value();
+}
+
+static double nanosecondsSince(Clock::time_point start)
+{
+  return std::chrono::duration<double, std::nano>(Clock::now() - start).count();
+}
+
+static NSDictionary *memoryUsage()
+{
+  task_vm_info_data_t info{};
+  mach_msg_type_number_t count = TASK_VM_INFO_COUNT;
+  auto status = task_info(mach_task_self(), TASK_VM_INFO, reinterpret_cast<task_info_t>(&info), &count);
+  if (status != KERN_SUCCESS) {
+    return @{@"taskInfoError" : @(status)};
+  }
+  return @{@"residentBytes" : @(info.resident_size), @"physicalFootprintBytes" : @(info.phys_footprint)};
+}
+
+static std::vector<ColorStop> inputForCase(const std::string &name)
+{
+  auto red = colorFromRGBA(255, 0, 0, 255);
+  auto blue = colorFromRGBA(0, 0, 255, 127);
+  if (name == "two_stops") {
+    return {{red, {}}, {blue, {}}};
+  }
+  if (name == "asymmetric_hint") {
+    return {{red, {0, UnitType::Percent}}, {{}, {15, UnitType::Percent}}, {blue, {100, UnitType::Percent}}};
+  }
+  std::vector<ColorStop> result;
+  if (name == "implicit_16" || name == "explicit_64") {
+    const int count = name == "implicit_16" ? 16 : 64;
+    for (int i = 0; i < count; ++i) {
+      ValueUnit position = count == 16 ? ValueUnit{} : ValueUnit{100.f * i / (count - 1), UnitType::Percent};
+      result.push_back({i % 2 == 0 ? red : blue, position});
+    }
+    return result;
+  }
+  if (name == "multiple_hints") {
+    for (int i = 0; i < 8; ++i) {
+      result.push_back({i % 2 == 0 ? red : blue, {100.f * i / 7, UnitType::Percent}});
+      if (i < 7) {
+        result.push_back({{}, {100.f * (i + 0.3f) / 7, UnitType::Percent}});
+      }
+    }
+    return result;
+  }
+  fprintf(stderr, "Unknown gradient benchmark case: %s\n", name.c_str());
+  exit(1);
+}
+
+int main(int argc, char **argv)
+{
+  const bool firstCallOnly = argc == 5 && std::string(argv[4]) == "--first-call-only";
+  if (argc != 4 && !firstCallOnly) {
+    fprintf(stderr, "Usage: AppleGradientBenchmark CASE ITERATIONS SAMPLES [--first-call-only]\n");
+    return 1;
+  }
+  char *iterationsEnd = nullptr;
+  char *samplesEnd = nullptr;
+  const auto iterations = strtoul(argv[2], &iterationsEnd, 10);
+  const auto samples = strtoul(argv[3], &samplesEnd, 10);
+  if (*iterationsEnd != '\0' || *samplesEnd != '\0' || iterations == 0 || iterations > 1000000 || samples == 0 ||
+      samples > 100) {
+    fprintf(stderr, "Iterations must be 1..1000000; samples must be 1..100.\n");
+    return 1;
+  }
+  @autoreleasepool {
+    auto input = inputForCase(argv[1]);
+    auto beforeFirstCall = memoryUsage();
+    auto start = Clock::now();
+    @autoreleasepool {
+      calculate(input);
+    }
+    const auto firstCallNanoseconds = nanosecondsSince(start);
+    auto afterFirstCall = memoryUsage();
+    const int warmupCalls = firstCallOnly ? 0 : 1000;
+    for (int i = 0; i < warmupCalls; ++i) {
+      @autoreleasepool {
+        calculate(input);
+      }
+    }
+    auto afterWarmup = memoryUsage();
+    NSMutableArray<NSNumber *> *timings = [NSMutableArray new];
+    for (unsigned long sample = 0; sample < (firstCallOnly ? 0 : samples); ++sample) {
+      start = Clock::now();
+      for (unsigned long iteration = 0; iteration < iterations; ++iteration) {
+        @autoreleasepool {
+          calculate(input);
+        }
+      }
+      [timings addObject:@(nanosecondsSince(start) / iterations)];
+    }
+    auto afterMeasurement = memoryUsage();
+    NSDictionary *result = @{
+      @"variant" : RCT_BENCHMARK_KMP ? @"kmp" : @"native",
+      @"case" : @(argv[1]),
+      @"iterationsPerSample" : @(iterations),
+      @"warmupCalls" : @(warmupCalls),
+      @"firstCallNanoseconds" : @(firstCallNanoseconds),
+      @"nanosecondsPerCall" : timings,
+      @"memoryBeforeFirstCall" : beforeFirstCall,
+      @"memoryAfterFirstCall" : afterFirstCall,
+      @"memoryAfterWarmup" : afterWarmup,
+      @"memoryAfterMeasurement" : afterMeasurement,
+      @"checksum" : @(checksum),
+    };
+    NSError *error = nil;
+    NSData *json = [NSJSONSerialization dataWithJSONObject:result options:NSJSONWritingPrettyPrinted error:&error];
+    if (json == nil) {
+      fprintf(stderr, "Unable to serialize benchmark result: %s\n", error.localizedDescription.UTF8String);
+      return 1;
+    }
+    fwrite(json.bytes, 1, json.length, stdout);
+    putchar('\n');
+  }
+  return 0;
+}
diff --git a/packages/react-native/ReactShared/tests/AppleGradientParity.mm b/packages/react-native/ReactShared/tests/AppleGradientParity.mm
new file mode 100644
index 000000000000..8b8350298805
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/AppleGradientParity.mm
@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <React/RCTGradientUtils.h>
+#import <react/renderer/graphics/RCTPlatformColorUtils.h>
+
+#include <cmath>
+#include <cstdio>
+#include <cstdlib>
+#include <random>
+
+using namespace facebook::react;
+
+// The test runner compiles the unchanged native path under this class name.
+@interface RCTGradientUtilsBaseline : NSObject
++ (std::vector<ProcessedColorStop>)getFixedColorStops:(const std::vector<ColorStop> &)colorStops
+                                   gradientLineLength:(CGFloat)gradientLineLength;
+@end
+
+static size_t checkedCases = 0;
+
+static void checkParity(const std::vector<ColorStop> &input, CGFloat lineLength = 240)
+{
+  auto expected = [RCTGradientUtilsBaseline getFixedColorStops:input gradientLineLength:lineLength];
+  auto actual = [RCTGradientUtils getFixedColorStops:input gradientLineLength:lineLength];
+  if (expected.size() != actual.size()) {
+    fprintf(stderr, "Gradient case %zu: expected %zu stops, got %zu\n", checkedCases, expected.size(), actual.size());
+    exit(1);
+  }
+  for (size_t i = 0; i < expected.size(); ++i) {
+    if (std::abs(expected[i].position.value() - actual[i].position.value()) > 1e-12 ||
+        static_cast<bool>(expected[i].color) != static_cast<bool>(actual[i].color) ||
+        (expected[i].color && (*expected[i].color).getColor() != (*actual[i].color).getColor())) {
+      fprintf(
+          stderr,
+          "Gradient case %zu: stop %zu differs (positions %.9g / %.9g, colors %x / %x)\n",
+          checkedCases,
+          i,
+          expected[i].position.value(),
+          actual[i].position.value(),
+          expected[i].color ? (*expected[i].color).getColor() : 0,
+          actual[i].color ? (*actual[i].color).getColor() : 0);
+      exit(1);
+    }
+  }
+  ++checkedCases;
+}
+
+int main()
+{
+  @autoreleasepool {
+    auto red = colorFromRGBA(255, 0, 0, 255);
+    auto blue = colorFromRGBA(0, 0, 255, 127);
+    auto green = colorFromRGBA(0, 255, 0, 255);
+    checkParity({});
+    checkParity({{red, {}}});
+    checkParity({{red, {}}, {green, {}}, {blue, {}}});
+    checkParity({{red, {75, UnitType::Percent}}, {green, {25, UnitType::Percent}}, {blue, {}}});
+    checkParity({{red, {-50, UnitType::Percent}}, {green, {}}, {blue, {150, UnitType::Percent}}});
+    checkParity({{red, {10, UnitType::Point}}, {green, {}}, {blue, {220, UnitType::Point}}});
+    // CGFloat precision matters here: Float rounding crosses the centered-hint epsilon.
+    checkParity({{red, {0, UnitType::Point}}, {{}, {100.5f, UnitType::Point}}, {blue, {200, UnitType::Point}}}, 200);
+
+    // Symmetric, endpoint, near-epsilon and asymmetric transition hints.
+    for (float hint : {0.f, 0.49f, 0.51f, 1.f, 20.f, 49.8f, 50.f, 50.2f, 80.f, 99.49f, 99.51f, 100.f}) {
+      checkParity({{red, {0, UnitType::Percent}}, {{}, {hint, UnitType::Percent}}, {blue, {100, UnitType::Percent}}});
+    }
+    checkParity(
+        {{red, {0, UnitType::Percent}},
+         {{}, {15, UnitType::Percent}},
+         {green, {40, UnitType::Percent}},
+         {{}, {85, UnitType::Percent}},
+         {blue, {100, UnitType::Percent}}});
+
+    // Retaining an original stop must retain its native dynamic color object.
+    SharedColor dynamicColor{Color(
+        DynamicColor{.lightColor = static_cast<int32_t>(0xffff0000), .darkColor = static_cast<int32_t>(0xff0000ff)})};
+    auto dynamicResult = [RCTGradientUtils getFixedColorStops:{
+      {dynamicColor, {}},
+      {blue, {}}
+    }
+                                           gradientLineLength:240];
+    if ((*dynamicResult[0].color).getUIColor() != (*dynamicColor).getUIColor()) {
+      fprintf(stderr, "KMP gradient adapter replaced an original dynamic UIColor\n");
+      return 1;
+    }
+    checkParity({{dynamicColor, {}}, {blue, {}}});
+
+    std::mt19937 random(8675309);
+    for (int i = 0; i < 250; ++i) {
+      float hint = 1 + random() % 99;
+      auto left = colorFromRGBA(random() % 256, random() % 256, random() % 256, random() % 256);
+      auto right = colorFromRGBA(random() % 256, random() % 256, random() % 256, random() % 256);
+      checkParity({{left, {0, UnitType::Percent}}, {{}, {hint, UnitType::Percent}}, {right, {100, UnitType::Percent}}});
+      checkParity(
+          {{left, {0, UnitType::Point}}, {{}, {hint * 1.7f, UnitType::Point}}, {right, {170, UnitType::Point}}},
+          237.25);
+    }
+    printf("Apple gradient parity passed: %zu cases; native colors and KMP positions/weights agree.\n", checkedCases);
+  }
+  return 0;
+}
diff --git a/packages/react-native/ReactShared/tests/AppleMultipartParity.m b/packages/react-native/ReactShared/tests/AppleMultipartParity.m
new file mode 100644
index 000000000000..df627767a9d1
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/AppleMultipartParity.m
@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <Foundation/Foundation.h>
+#import <QuartzCore/QuartzCore.h>
+#import <React/RCTMultipartStreamReader.h>
+
+@interface RCTMultipartStreamReaderBaseline : NSObject
+- (instancetype)initWithInputStream:(NSInputStream *)stream boundary:(NSString *)boundary;
+- (BOOL)readAllPartsWithCompletionCallback:(RCTMultipartCallback)callback
+                          progressCallback:(RCTMultipartProgressCallback)progressCallback;
+@end
+
+@interface FragmentedMultipartStream : NSInputStream
+- (instancetype)initWithData:(NSData *)data readSize:(NSUInteger)readSize;
+@end
+
+@implementation FragmentedMultipartStream {
+  NSData *_data;
+  NSUInteger _offset;
+  NSUInteger _readSize;
+}
+- (instancetype)initWithData:(NSData *)data readSize:(NSUInteger)readSize
+{
+  if (self = [super init]) {
+    _data = data;
+    _readSize = readSize;
+  }
+  return self;
+}
+- (void)open
+{
+}
+- (NSError *)streamError
+{
+  return nil;
+}
+- (NSInteger)read:(uint8_t *)buffer maxLength:(NSUInteger)length
+{
+  NSUInteger count = MIN(MIN(length, _readSize), _data.length - _offset);
+  [_data getBytes:buffer range:NSMakeRange(_offset, count)];
+  _offset += count;
+  return count;
+}
+@end
+
+static NSDictionary *Read(Class readerClass, NSData *data, NSUInteger readSize, BOOL retainBodies)
+{
+  NSInputStream *stream = [[FragmentedMultipartStream alloc] initWithData:data readSize:readSize];
+  RCTMultipartStreamReader *reader = [[readerClass alloc] initWithInputStream:stream boundary:@"sample"];
+  NSMutableArray *parts = [NSMutableArray new];
+  NSMutableArray *completedProgress = [NSMutableArray new];
+  __block NSArray *progress;
+  BOOL success = [reader
+      readAllPartsWithCompletionCallback:^(NSDictionary *headers, NSData *body, BOOL done) {
+        [parts addObject:@[ headers ?: @{}, retainBodies ? (id)body : @(body.length), @(done) ]];
+        [completedProgress addObject:progress ?: @[]];
+        progress = nil;
+      }
+      progressCallback:^(NSDictionary *headers, NSNumber *length, NSNumber *loaded) {
+        progress = @[ headers, length, loaded ];
+      }];
+  return @{@"success" : @(success), @"parts" : parts, @"finalProgress" : completedProgress};
+}
+
+static void Require(BOOL condition, NSString *message)
+{
+  if (!condition) {
+    fprintf(stderr, "FAIL: %s\n", message.UTF8String);
+    exit(1);
+  }
+}
+
+static NSData *Response(NSUInteger size)
+{
+  NSMutableData *data = [[NSString stringWithFormat:@"preamble\r\n--sample\r\nContent-Length: %lu\r\n\r\n",
+                                                    (unsigned long)size] dataUsingEncoding:NSUTF8StringEncoding]
+                            .mutableCopy;
+  NSMutableData *body = [NSMutableData dataWithLength:size];
+  // Deterministic binary content, without a valid delimiter or header separator.
+  uint8_t *bytes = body.mutableBytes;
+  for (NSUInteger i = 0; i < size; i++)
+    bytes[i] = (uint8_t)(i % 251);
+  [data appendData:body];
+  [data appendData:[@"\r\n--sample--\r\nepilogue" dataUsingEncoding:NSUTF8StringEncoding]];
+  return data;
+}
+
+static double Measure(Class readerClass, NSData *data, NSUInteger size)
+{
+  CFTimeInterval start = CACurrentMediaTime();
+  @autoreleasepool {
+    NSDictionary *result = Read(readerClass, data, 4096, NO);
+    Require([result[@"success"] boolValue], @"benchmark completion");
+    Require(
+        [result[@"parts"] count] == 1 && [result[@"parts"][0][1] unsignedIntegerValue] == size,
+        @"benchmark body length");
+  }
+  return (CACurrentMediaTime() - start) * 1000;
+}
+
+int main(int argc, const char *argv[])
+{
+  @autoreleasepool {
+    Class native = RCTMultipartStreamReaderBaseline.class;
+    Class shared = RCTMultipartStreamReader.class;
+    if (argc == 2 && strcmp(argv[1], "--benchmark") == 0) {
+      for (NSNumber *megabytes in @[ @2, @20 ]) {
+        NSUInteger size = megabytes.unsignedIntegerValue * 1024 * 1024;
+        NSData *data = Response(size);
+        Require([Read(native, data, 4096, YES) isEqual:Read(shared, data, 4096, YES)], @"large body exact parity");
+        for (NSUInteger i = 0; i < 5; i++) {
+          Measure(native, data, size);
+          Measure(shared, data, size);
+        }
+        NSMutableArray *nativeSamples = [NSMutableArray new];
+        NSMutableArray *sharedSamples = [NSMutableArray new];
+        for (NSUInteger i = 0; i < 21; i++) {
+          if (i % 2 == 0) {
+            [nativeSamples addObject:@(Measure(native, data, size))];
+            [sharedSamples addObject:@(Measure(shared, data, size))];
+          } else {
+            [sharedSamples addObject:@(Measure(shared, data, size))];
+            [nativeSamples addObject:@(Measure(native, data, size))];
+          }
+        }
+        double baseline = [[nativeSamples sortedArrayUsingSelector:@selector(compare:)][10] doubleValue];
+        double kmp = [[sharedSamples sortedArrayUsingSelector:@selector(compare:)][10] doubleValue];
+        NSDictionary *result = @{
+          @"bytes" : @(size),
+          @"iterations" : @21,
+          @"nativeMedianMs" : @(baseline),
+          @"kmpMedianMs" : @(kmp),
+          @"ratio" : @(kmp / baseline),
+          @"nativeSamplesMs" : nativeSamples,
+          @"kmpSamplesMs" : sharedSamples
+        };
+        puts([[NSString alloc] initWithData:[NSJSONSerialization dataWithJSONObject:result options:0 error:nil]
+                                   encoding:NSUTF8StringEncoding]
+                 .UTF8String);
+      }
+      return 0;
+    }
+
+    NSArray *inputs = @[
+      @"Yolo",
+      @"preamble\r\n--sample--\r\n",
+      @"\r\n--sample\r\none\r\n--sample\r\ntwo\r\n--sample--\r\nepilogue",
+      @"\r\n--sample\r\nX: a:b\r\nx: c\r\n invalid \r\n\r\nbody\r\n--sample--\r\n",
+      @"\r\n--sample\r\nfirst\r\n--sample\r\nincomplete",
+      @"\r\n--sample\r\nbinary\0\r\n--samplX\r\n--sample-\r\n--sample--\r\n"
+    ];
+    NSUInteger cases = 0;
+    for (NSString *input in inputs) {
+      NSData *data = [input dataUsingEncoding:NSUTF8StringEncoding];
+      for (NSUInteger readSize = 1; readSize <= data.length; readSize++) {
+        Require(
+            [Read(native, data, readSize, YES) isEqual:Read(shared, data, readSize, YES)],
+            [NSString stringWithFormat:@"native/KMP parity case %lu read %lu",
+                                       (unsigned long)cases,
+                                       (unsigned long)readSize]);
+        cases++;
+      }
+    }
+    for (NSNumber *size in @[ @4095, @4096, @4097, @65536 ]) {
+      NSData *data = Response(size.unsignedIntegerValue);
+      Require([Read(native, data, 4096, YES) isEqual:Read(shared, data, 4096, YES)], @"binary body/progress parity");
+      cases++;
+    }
+    printf("PASS: %lu real Apple multipart adapter parity cases\n", (unsigned long)cases);
+  }
+  return 0;
+}
diff --git a/packages/react-native/ReactShared/tests/AppleScrollSnapParity.mm b/packages/react-native/ReactShared/tests/AppleScrollSnapParity.mm
new file mode 100644
index 000000000000..7151fbc1e3a9
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/AppleScrollSnapParity.mm
@@ -0,0 +1,181 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <React/RCTEnhancedScrollView.h>
+#import <React/RCTUtils.h>
+#import <mach/mach_time.h>
+#include <cmath>
+#include <cstdio>
+#include <cstdlib>
+#include <initializer_list>
+
+// This fixture links the actual scroll view and delegate splitter. The only omitted
+// implementation is RN's logging sanitizer; every test coordinate is finite.
+double RCTSanitizeNaNValue(double value, NSString *property)
+{
+  if (!std::isfinite(value)) {
+    std::abort();
+  }
+  return value;
+}
+
+static RCTEnhancedScrollView *makeView(NSString *className, BOOL horizontal)
+{
+  auto view = (RCTEnhancedScrollView *)[[NSClassFromString(className) alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
+  if (!view) {
+    std::abort();
+  }
+  view.contentSize = horizontal ? CGSizeMake(500, 200) : CGSizeMake(200, 500);
+  view.snapToStart = YES;
+  view.snapToEnd = YES;
+  return view;
+}
+
+static CGPoint target(RCTEnhancedScrollView *view, BOOL horizontal, double predicted, double velocity)
+{
+  CGPoint result = horizontal ? CGPointMake(predicted, 17) : CGPointMake(17, predicted);
+  CGPoint speed = horizontal ? CGPointMake(velocity, 0) : CGPointMake(0, velocity);
+  [(id<UIScrollViewDelegate>)view scrollViewWillEndDragging:view withVelocity:speed targetContentOffset:&result];
+  return result;
+}
+
+static void requireEqual(CGPoint actual, CGPoint expected, NSUInteger index)
+{
+  if (actual.x != expected.x || actual.y != expected.y) {
+    std::fprintf(
+        stderr, "case %lu: (%g, %g) != (%g, %g)\n", (unsigned long)index, actual.x, actual.y, expected.x, expected.y);
+    std::exit(1);
+  }
+}
+
+static void checkViews(
+    RCTEnhancedScrollView *actual,
+    RCTEnhancedScrollView *baseline,
+    RCTEnhancedScrollView *cached,
+    BOOL horizontal,
+    double predicted,
+    double velocity,
+    NSUInteger index)
+{
+  auto expected = target(baseline, horizontal, predicted, velocity);
+  requireEqual(target(actual, horizontal, predicted, velocity), expected, index);
+  requireEqual(target(cached, horizontal, predicted, velocity), expected, index);
+}
+
+static double nanos(uint64_t elapsed)
+{
+  mach_timebase_info_data_t scale;
+  mach_timebase_info(&scale);
+  return (double)elapsed * scale.numer / scale.denom;
+}
+
+int main(int argc, const char **argv)
+{
+  @autoreleasepool {
+#if RCT_SCROLL_BENCHMARK
+    const NSUInteger count = argc > 1 ? strtoul(argv[1], nullptr, 10) : 16;
+    const NSUInteger iterations = 10000;
+    auto view = makeView(@"RCTEnhancedScrollView", YES);
+    NSMutableArray<NSNumber *> *offsets = [NSMutableArray new];
+    for (NSUInteger i = 0; i < count; i++) {
+      [offsets addObject:@(300.0 * i / MAX(count - 1, 1UL))];
+    }
+    const auto propertyStart = mach_continuous_time();
+    view.snapToOffsets = offsets;
+    const double firstPropertyNanos = nanos(mach_continuous_time() - propertyStart);
+    const auto firstStart = mach_continuous_time();
+    auto first = target(view, YES, 151.0, 1.0);
+    const double firstFlingNanos = nanos(mach_continuous_time() - firstStart);
+    NSMutableArray<NSNumber *> *samples = [NSMutableArray new];
+    double checksum = first.x;
+    for (NSUInteger sample = 0; sample < 7; sample++) {
+      const auto start = mach_continuous_time();
+      for (NSUInteger i = 0; i < iterations; i++) {
+        @autoreleasepool {
+          checksum += target(view, YES, (double)(i % 301), (int)(i % 3) - 1).x;
+        }
+      }
+      [samples addObject:@(nanos(mach_continuous_time() - start) / iterations)];
+    }
+    NSDictionary *report = @{
+      @"offsetCount" : @(count),
+      @"iterationsPerSample" : @(iterations),
+      @"firstPropertyNanos" : @(firstPropertyNanos),
+      @"firstFlingNanos" : @(firstFlingNanos),
+      @"nanosPerFling" : samples,
+      @"checksum" : @(checksum),
+    };
+#else
+    NSUInteger cases = 0;
+    NSArray<NSArray<NSNumber *> *> *lists = @[
+      @[],
+      @[ @60 ],
+      @[ @20, @60, @100 ],
+      @[ @0.25, @0.25, @60.1, @100.75 ],
+      @[ @100, @20, @60 ],
+      @[ @-20, @60, @350 ],
+    ];
+    for (BOOL horizontal : {NO, YES}) {
+      auto actual = makeView(@"RCTEnhancedScrollView", horizontal);
+      auto baseline = makeView(@"RCTEnhancedScrollViewBaseline", horizontal);
+      auto cached = makeView(@"RCTEnhancedScrollViewCached", horizontal);
+      for (double maximum : {0.0, 120.0, 300.0}) {
+        actual.contentSize = baseline.contentSize = cached.contentSize =
+            horizontal ? CGSizeMake(200 + maximum, 200) : CGSizeMake(200, 200 + maximum);
+        for (NSArray<NSNumber *> *offsets in lists) {
+          actual.snapToOffsets = baseline.snapToOffsets = cached.snapToOffsets = offsets;
+          for (int flags = 0; flags < 4; flags++) {
+            actual.snapToStart = baseline.snapToStart = cached.snapToStart = flags & 1;
+            actual.snapToEnd = baseline.snapToEnd = cached.snapToEnd = flags & 2;
+            for (double current : {-20.0, 0.0, 20.0, 60.0, 100.0, 150.0, 320.0}) {
+              actual.contentOffset = baseline.contentOffset = cached.contentOffset =
+                  horizontal ? CGPointMake(current, 0) : CGPointMake(0, current);
+              for (double predicted : {-50.0, 0.0, 20.0, 39.9, 40.0, 60.0, 100.0, 120.0, 150.0, 320.0}) {
+                for (double velocity : {-1.0, 0.0, 1.0}) {
+                  checkViews(actual, baseline, cached, horizontal, predicted, velocity, ++cases);
+                }
+              }
+            }
+          }
+        }
+      }
+      // Replacing/clearing the property must invalidate the cached selector.
+      NSMutableArray<NSNumber *> *mutableOffsets = [@[ @20, @60, @100 ] mutableCopy];
+      actual.snapToOffsets = baseline.snapToOffsets = cached.snapToOffsets = mutableOffsets;
+      mutableOffsets[1] = @90;
+      checkViews(actual, baseline, cached, horizontal, 40, 1, ++cases);
+      for (NSArray<NSNumber *> *replacement in @[ @[ @30, @70 ], @[] ]) {
+        actual.snapToOffsets = baseline.snapToOffsets = cached.snapToOffsets = replacement;
+        checkViews(actual, baseline, cached, horizontal, 40, 1, ++cases);
+      }
+      [actual setValue:nil forKey:@"snapToOffsets"];
+      [baseline setValue:nil forKey:@"snapToOffsets"];
+      [cached setValue:nil forKey:@"snapToOffsets"];
+      // Interval snapping remains a native operation, including alignment and momentum policy.
+      actual.contentSize = baseline.contentSize = cached.contentSize =
+          horizontal ? CGSizeMake(500, 200) : CGSizeMake(200, 500);
+      actual.snapToInterval = baseline.snapToInterval = cached.snapToInterval = 60;
+      actual.contentOffset = baseline.contentOffset = cached.contentOffset =
+          horizontal ? CGPointMake(75, 0) : CGPointMake(0, 75);
+      for (NSString *alignment in @[ @"start", @"center", @"end" ]) {
+        actual.snapToAlignment = baseline.snapToAlignment = cached.snapToAlignment = alignment;
+        for (BOOL disableMomentum : {NO, YES}) {
+          actual.disableIntervalMomentum = baseline.disableIntervalMomentum = cached.disableIntervalMomentum =
+              disableMomentum;
+          for (double velocity : {-1.0, 0.0, 1.0}) {
+            checkViews(actual, baseline, cached, horizontal, 130, velocity, ++cases);
+          }
+        }
+      }
+    }
+    NSDictionary *report = @{@"passedCases" : @(cases), @"cachedNativeControlCases" : @(cases), @"failedCases" : @0};
+#endif
+    NSData *json = [NSJSONSerialization dataWithJSONObject:report options:NSJSONWritingSortedKeys error:nil];
+    std::puts([[NSString alloc] initWithData:json encoding:NSUTF8StringEncoding].UTF8String);
+  }
+  return 0;
+}
diff --git a/packages/react-native/ReactShared/tests/coexistence/AppleKotlinCoexistence.mm b/packages/react-native/ReactShared/tests/coexistence/AppleKotlinCoexistence.mm
new file mode 100644
index 000000000000..eeff8e3e198c
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/coexistence/AppleKotlinCoexistence.mm
@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <IndependentKotlin/IndependentKotlin.h>
+#import <ReactNativeShared/ReactNativeShared.h>
+#import <dispatch/dispatch.h>
+
+#include <cstdio>
+#include <cstdlib>
+
+extern "C" NSArray<RNSResolvedGradientStop *> *ReactNativeSharedFixtureStops();
+
+static void check(bool condition, const char *message)
+{
+  if (!condition) {
+    fprintf(stderr, "Kotlin framework coexistence failed: %s\n", message);
+    abort();
+  }
+}
+
+static void exercise(int32_t seed)
+{
+  // Each framework keeps ownership of its Kotlin objects. Only primitive values
+  // are copied between their APIs; these are not cast across Kotlin runtimes.
+  auto independent = IndependentKotlinIndependentProbe.shared;
+  auto token = [independent makeTokenSeed:seed];
+  auto stops = ReactNativeSharedFixtureStops();
+  check(stops.count == 3, "shared resolver returned the wrong number of stops");
+  @autoreleasepool {
+    NSArray *values = @[
+      [[IndependentKotlinDouble alloc] initWithDouble:stops[0].position],
+      [[IndependentKotlinDouble alloc] initWithDouble:stops[1].position],
+      [[IndependentKotlinDouble alloc] initWithDouble:stops[2].position],
+    ];
+    check([independent sumValues:values] == 1.5, "independent framework could not use copied numeric values");
+    for (int i = 0; i < 10; ++i) {
+      @autoreleasepool {
+        check(ReactNativeSharedFixtureStops().count == 3, "shared framework changed while another framework was alive");
+        check(
+            [independent verifyTokenToken:[independent makeTokenSeed:i] seed:i],
+            "independent token did not round-trip");
+      }
+    }
+  }
+  check(stops[1].position == 0.5, "retained shared result changed after inner autorelease pools drained");
+  check([independent verifyTokenToken:token seed:seed], "retained independent object lost its state");
+}
+
+int main()
+{
+  @autoreleasepool {
+    for (int32_t i = 0; i < 100; ++i) {
+      @autoreleasepool {
+        exercise(i);
+      }
+    }
+    dispatch_apply(64, dispatch_get_global_queue(QOS_CLASS_DEFAULT, 0), ^(size_t index) {
+      @autoreleasepool {
+        exercise(static_cast<int32_t>(index));
+      }
+    });
+    puts("Kotlin framework coexistence passed: 100 serial and 64 concurrent object-lifetime/value checks.");
+  }
+  return 0;
+}
diff --git a/packages/react-native/ReactShared/tests/coexistence/IndependentKotlin.kt b/packages/react-native/ReactShared/tests/coexistence/IndependentKotlin.kt
new file mode 100644
index 000000000000..a54d9403a43d
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/coexistence/IndependentKotlin.kt
@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared.fixture
+
+// Deliberately compiled as an independent framework, without ReactNativeShared.
+public class IndependentToken(public val value: String)
+
+public object IndependentProbe {
+  public fun makeToken(seed: Int): IndependentToken = IndependentToken("independent-$seed")
+
+  public fun verifyToken(token: IndependentToken, seed: Int): Boolean =
+      token.value == "independent-$seed"
+
+  public fun sum(values: List<Double>): Double = values.sum()
+}
diff --git a/packages/react-native/ReactShared/tests/coexistence/ReactNativeRuntimeOwner.mm b/packages/react-native/ReactShared/tests/coexistence/ReactNativeRuntimeOwner.mm
new file mode 100644
index 000000000000..16e7403c84d8
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/coexistence/ReactNativeRuntimeOwner.mm
@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <ReactNativeShared/ReactNativeShared.h>
+
+// Linked into the host for static React Native, or into one dedicated dylib for
+// dynamic React Native. The dynamic host never links ReactNativeShared again.
+extern "C" NSArray<RNSResolvedGradientStop *> *ReactNativeSharedFixtureStops()
+{
+  NSArray *input = @[
+    [[RNSGradientStopInput alloc] initWithPosition:nil hasColor:YES],
+    [[RNSGradientStopInput alloc] initWithPosition:nil hasColor:YES],
+    [[RNSGradientStopInput alloc] initWithPosition:nil hasColor:YES],
+  ];
+  return [RNSGradientStops.shared resolveStops:input epsilon:0.005 useDoublePrecision:YES];
+}
diff --git a/packages/react-native/ReactShared/tests/distribution/Package.swift b/packages/react-native/ReactShared/tests/distribution/Package.swift
new file mode 100644
index 000000000000..f4b166522094
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/distribution/Package.swift
@@ -0,0 +1,25 @@
+// swift-tools-version: 6.0
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import PackageDescription
+
+let package = Package(
+  name: "KMPDistributionProbe",
+  platforms: [.iOS(.v15), .macCatalyst(.v15)],
+  products: [.library(name: "KMPDistributionProbe", type: .dynamic, targets: ["Probe"])],
+  targets: [
+    .binaryTarget(name: "ReactNativeShared", path: "ReactNativeShared.xcframework"),
+    .target(
+      name: "Probe",
+      dependencies: [.target(name: "ReactNativeShared", condition: .when(platforms: [.iOS]))],
+      cSettings: [.unsafeFlags(["-fobjc-arc"])],
+      linkerSettings: [.linkedFramework("Foundation")]
+    ),
+    .testTarget(name: "ProbeTests", dependencies: ["Probe"]),
+  ]
+)
diff --git a/packages/react-native/ReactShared/tests/distribution/Sources/Probe/Probe.m b/packages/react-native/ReactShared/tests/distribution/Sources/Probe/Probe.m
new file mode 100644
index 000000000000..00cb0052e629
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/distribution/Sources/Probe/Probe.m
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "Probe.h"
+#import <TargetConditionals.h>
+
+#if !TARGET_OS_MACCATALYST
+#import <ReactNativeShared/ReactNativeShared.h>
+#endif
+
+int RNSDistributionProbe(void)
+{
+#if TARGET_OS_MACCATALYST
+  return 1;
+#else
+  @autoreleasepool {
+    NSArray *input = @[
+      [[RNSGradientStopInput alloc] initWithPosition:nil hasColor:YES],
+      [[RNSGradientStopInput alloc] initWithPosition:nil hasColor:YES],
+      [[RNSGradientStopInput alloc] initWithPosition:nil hasColor:YES],
+    ];
+    NSArray<RNSResolvedGradientStop *> *stops = [RNSGradientStops.shared resolveStops:input
+                                                                              epsilon:0.00001
+                                                                   useDoublePrecision:YES];
+    return stops.count == 3 && stops[0].position == 0 && stops[1].position == 0.5 && stops[2].position == 1 &&
+        stops[1].leftColorIndex == 1;
+  }
+#endif
+}
diff --git a/packages/react-native/ReactShared/tests/distribution/Sources/Probe/include/Probe.h b/packages/react-native/ReactShared/tests/distribution/Sources/Probe/include/Probe.h
new file mode 100644
index 000000000000..05ea4b723bc9
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/distribution/Sources/Probe/include/Probe.h
@@ -0,0 +1,8 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+int RNSDistributionProbe(void);
diff --git a/packages/react-native/ReactShared/tests/distribution/Tests/ProbeTests/ProbeTests.swift b/packages/react-native/ReactShared/tests/distribution/Tests/ProbeTests/ProbeTests.swift
new file mode 100644
index 000000000000..e116f7df5f42
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/distribution/Tests/ProbeTests/ProbeTests.swift
@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import Probe
+import XCTest
+
+final class ProbeTests: XCTestCase {
+  func testPackagedGradientCalculation() {
+    XCTAssertEqual(RNSDistributionProbe(), 1)
+  }
+}
diff --git a/packages/react-native/ReactShared/tests/smoke/AppleKmpSmoke.mm b/packages/react-native/ReactShared/tests/smoke/AppleKmpSmoke.mm
new file mode 100644
index 000000000000..9227fd266193
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/smoke/AppleKmpSmoke.mm
@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <ReactNativeShared/ReactNativeShared.h>
+
+#include <cstdint>
+#include <cstdio>
+
+int main()
+{
+  @autoreleasepool {
+    struct Case {
+      int32_t left;
+      int32_t right;
+      int32_t expected;
+    };
+    const Case cases[] = {{19, 23, 42}, {-7, 4, -3}, {0, 0, 0}, {INT32_MAX, 0, INT32_MAX}, {INT32_MIN, 0, INT32_MIN}};
+    for (const auto &test : cases) {
+      if ([RNSKmpSmoke.shared addLeft:test.left right:test.right] != test.expected) {
+        fprintf(stderr, "Kotlin Objective-C integer interop failed\n");
+        return 1;
+      }
+    }
+    puts("Kotlin Objective-C smoke passed: 5 cases");
+  }
+  return 0;
+}
diff --git a/packages/react-native/ReactShared/tests/smoke/kotlin/KmpSmoke.kt b/packages/react-native/ReactShared/tests/smoke/kotlin/KmpSmoke.kt
new file mode 100644
index 000000000000..f8e52f414e2a
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/smoke/kotlin/KmpSmoke.kt
@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared.smoke
+
+// Unpublished compiler/interop fixture, included only with reactNativeSharedSmoke=true.
+public object KmpSmoke {
+  public fun add(left: Int, right: Int): Int = left + right
+}
diff --git a/packages/react-native/ReactShared/tests/smoke/kotlinTest/KmpSmokeTest.kt b/packages/react-native/ReactShared/tests/smoke/kotlinTest/KmpSmokeTest.kt
new file mode 100644
index 000000000000..73325f799788
--- /dev/null
+++ b/packages/react-native/ReactShared/tests/smoke/kotlinTest/KmpSmokeTest.kt
@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.shared.smoke
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class KmpSmokeTest {
+  @Test
+  fun positiveIntegers() {
+    assertEquals(42, KmpSmoke.add(19, 23))
+  }
+
+  @Test
+  fun signedIntegers() {
+    assertEquals(-3, KmpSmoke.add(-7, 4))
+  }
+
+  @Test
+  fun zero() {
+    assertEquals(0, KmpSmoke.add(0, 0))
+  }
+
+  @Test
+  fun integerBoundaries() {
+    assertEquals(Int.MAX_VALUE, KmpSmoke.add(Int.MAX_VALUE, 0))
+    assertEquals(Int.MIN_VALUE, KmpSmoke.add(Int.MIN_VALUE, 0))
+  }
+}
diff --git a/packages/react-native/package.json b/packages/react-native/package.json
index a09745bf963c..3c0c18ef6032 100644
--- a/packages/react-native/package.json
+++ b/packages/react-native/package.json
@@ -93,6 +93,19 @@
     "!ReactAndroid/src/test",
     "ReactApple",
     "ReactCommon",
+    "ReactShared/*.gradle.kts",
+    "ReactShared/*.podspec",
+    "ReactShared/cocoapods",
+    "ReactShared/gradle.properties",
+    "ReactShared/gradle/wrapper",
+    "ReactShared/gradlew",
+    "ReactShared/gradlew.bat",
+    "ReactShared/README.md",
+    "ReactShared/scripts",
+    "ReactShared/src",
+    "ReactShared/tests",
+    "!ReactShared/**/__pycache__",
+    "!ReactShared/**/*.pyc",
     "README.md",
     "scripts/replace-rncore-version.js",
     "scripts/bundle.js",
diff --git a/packages/react-native/scripts/cocoapods/kmp.rb b/packages/react-native/scripts/cocoapods/kmp.rb
new file mode 100644
index 000000000000..1d4ba752a8aa
--- /dev/null
+++ b/packages/react-native/scripts/cocoapods/kmp.rb
@@ -0,0 +1,133 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+class ReactNativeKMPUtils
+  def self.configure_aggregate_xcconfig(installer)
+    installer.aggregate_targets.each do |aggregate_target|
+      aggregate_target.xcconfigs.each do |config_name, config_file|
+        # CocoaPods excludes the host's static pods from search-path-only test
+        # targets here. user_target_xcconfig does not perform that exclusion.
+        linked_pods = aggregate_target.build_settings(config_name).pod_targets_to_link
+        next unless linked_pods.any? { |pod| pod.pod_name == 'React-KMP' }
+
+        # Dynamic React-Core already contains the static Kotlin runtime. Other
+        # consumers use their existing React-Core dependency to share that owner.
+        next if linked_pods.any? { |pod| pod.pod_name == 'React-Core' && pod.build_as_dynamic? }
+        %w[iphoneos iphonesimulator].each do |sdk|
+          # Full-pod sibling tests also reuse their host's runtime. Resolve each
+          # SDK separately because TEST_HOST and product settings can be conditional.
+          next if test_host_links_kmp?(aggregate_target, config_name, installer.aggregate_targets, sdk)
+
+          key = "OTHER_LDFLAGS[sdk=#{sdk}*]"
+          flags = config_file.attributes[key] || '$(inherited)'
+          unless flags.include?('-framework ReactNativeShared')
+            config_file.attributes[key] = "#{flags} -framework ReactNativeShared"
+          end
+        end
+        config_file.save_as(aggregate_target.xcconfig_path(config_name))
+      end
+    end
+  end
+
+  def self.test_host_links_kmp?(aggregate_target, config_name, aggregate_targets, sdk)
+    user_targets = aggregate_target.user_targets
+    !user_targets.empty? && user_targets.all? do |target|
+      next false unless target.symbol_type == :unit_test_bundle
+
+      settings = target_settings(target, config_name, sdk)
+      test_host = expand_build_setting(settings['TEST_HOST'], settings)
+      bundle_loader = expand_build_setting(settings['BUNDLE_LOADER'], settings)
+      next false if test_host.to_s.empty? || bundle_loader.to_s.empty?
+      next false unless Pathname.new(test_host).cleanpath == Pathname.new(bundle_loader).cleanpath
+
+      project = aggregate_target.user_project
+      host_uuid = project.root_object.attributes.dig('TargetAttributes', target.uuid, 'TestTargetID')
+      # TestTargetID is optional. A dependency is only a candidate, not evidence
+      # of hosting: both loader settings must identify its actual app executable.
+      candidates = host_uuid ? project.targets.select { |app| app.uuid == host_uuid } : target.dependencies.map(&:target).compact
+      hosts = candidates.select do |app|
+        next false unless app.project == project && app.symbol_type == :application
+        app_settings = target_settings(app, config_name, sdk)
+        executable = expand_build_setting(app_settings['EXECUTABLE_PATH'], app_settings)
+        next false if executable.to_s.empty? || executable.include?('$')
+        path = expand_build_setting("$(BUILT_PRODUCTS_DIR)/#{executable}", app_settings)
+        path && Pathname.new(path).cleanpath == Pathname.new(test_host).cleanpath
+      end
+      next false unless hosts.one?
+
+      aggregate_targets.any? do |candidate|
+        candidate.user_project == project && candidate.user_target_uuids.include?(hosts.first.uuid) &&
+          candidate.build_settings(config_name).pod_targets_to_link.any? { |pod| pod.pod_name == 'React-KMP' }
+      end
+    end
+  end
+
+  def self.target_settings(target, config_name, sdk)
+    # Xcodeproj's resolved_build_setting drops unknown SDK variables and does
+    # not supply product defaults. Preserve those variables for exact path matching.
+    settings = {
+      'TARGET_NAME' => target.name, 'CONFIGURATION' => config_name,
+      'PROJECT_NAME' => target.project.path.basename('.xcodeproj').to_s,
+      'SRCROOT' => target.project.project_dir.to_s, 'PROJECT_DIR' => target.project.project_dir.to_s,
+      'PRODUCT_NAME' => '$(TARGET_NAME)', 'EXECUTABLE_PREFIX' => '', 'EXECUTABLE_SUFFIX' => '',
+      'EXECUTABLE_NAME' => '$(EXECUTABLE_PREFIX)$(PRODUCT_NAME)$(EXECUTABLE_SUFFIX)',
+      'WRAPPER_NAME' => '$(PRODUCT_NAME).app', 'FULL_PRODUCT_NAME' => '$(WRAPPER_NAME)',
+      'EXECUTABLE_FOLDER_PATH' => '$(FULL_PRODUCT_NAME)',
+      'EXECUTABLE_PATH' => '$(EXECUTABLE_FOLDER_PATH)/$(EXECUTABLE_NAME)',
+      'BUNDLE_EXECUTABLE_FOLDER_PATH' => '',
+      'BUILT_PRODUCTS_DIR' => '$(CONFIGURATION_BUILD_DIR)',
+      'TARGET_BUILD_DIR' => '$(CONFIGURATION_BUILD_DIR)',
+    }
+    [target.project.build_configuration_list[config_name], target.build_configuration_list[config_name]].compact.each do |config|
+      path = config.base_configuration_reference&.real_path
+      xcconfig = path&.file? ? Xcodeproj::Config.new(path).to_hash : {}
+      [xcconfig, config.build_settings].each do |layer|
+        # Conditional values override their unqualified value within the layer.
+        uncertain = []
+        layer.sort_by { |key, _| key.count('[') }.each do |key, value|
+          next unless value.is_a?(String)
+          name = key.split('[').first
+          conditions = key.scan(/\[([^=]+)=([^\]]+)\]/).map do |qualifier, pattern|
+            case qualifier
+            when 'config' then File.fnmatch?(pattern, config_name)
+            when 'sdk'
+              if File.fnmatch?(pattern, sdk)
+                true
+              else
+                # A partial/version-specific match cannot be resolved at pod install.
+                prefix = pattern.split(/[*?\[]/, 2).first.to_s
+                (sdk.start_with?(prefix) || prefix.start_with?(sdk)) ? nil : false
+              end
+            end
+          end
+          next if conditions.include?(false)
+          # Do not guess the host if an unsupported qualifier affects its path.
+          uncertain << name if conditions.include?(nil)
+          inherited = /\$\(inherited\)|\$\{inherited\}/
+          unresolved_inheritance = settings.key?(name) && settings[name].nil? && value.match?(inherited)
+          settings[name] = unresolved_inheritance ? nil : value.gsub(inherited) { settings[name].to_s }
+        end
+        # Unknown precedence must not depend on the order of equally qualified keys.
+        uncertain.each { |name| settings[name] = nil }
+      end
+    end
+    settings
+  end
+
+  def self.expand_build_setting(value, settings, expanding = [])
+    return nil if value.nil?
+
+    value.to_s.sub(/\A(["'])(.*)\1\z/m, '\\2').gsub(/\$\((\w+)\)|\$\{(\w+)\}/) do
+      key = Regexp.last_match(1) || Regexp.last_match(2)
+      if settings.key?(key) && !expanding.include?(key)
+        expanded = expand_build_setting(settings[key], settings, expanding + [key])
+        return nil if expanded.nil?
+        expanded
+      else
+        "$(#{key})"
+      end
+    end
+  end
+end
diff --git a/packages/react-native/scripts/react_native_pods.rb b/packages/react-native/scripts/react_native_pods.rb
index c0c13480dadd..35cf97b2dbff 100644
--- a/packages/react-native/scripts/react_native_pods.rb
+++ b/packages/react-native/scripts/react_native_pods.rb
@@ -11,6 +11,7 @@
 require_relative './cocoapods/rndependencies.rb'
 require_relative './cocoapods/rncore.rb'
 require_relative './cocoapods/fabric.rb'
+require_relative './cocoapods/kmp.rb'
 require_relative './cocoapods/codegen.rb'
 require_relative './cocoapods/codegen_utils.rb'
 require_relative './cocoapods/utils.rb'
@@ -115,6 +116,11 @@ def use_react_native! (
   # Users can still turn them off and build from source by setting the environment variable to 0.
   ENV['RCT_USE_RN_DEP'] = ENV['RCT_USE_RN_DEP'] == '0' ? '0' : '1'
   ENV['RCT_USE_PREBUILT_RNCORE'] = ENV['RCT_USE_PREBUILT_RNCORE'] == '0' ? '0' : '1'
+  if ENV['RCT_USE_KMP'] == '1'
+    # The published core binaries do not contain the opt-in shared gradient adapter.
+    ENV['RCT_USE_PREBUILT_RNCORE'] = '0'
+    Pod::UI.puts 'React Native KMP pilot: building React Native core from source.'
+  end
   # Make `REMOVE_LEGACY_ARCH` enabled by default. This will build React Native
   # excluding the legacy arch unless the user turns this flag off explicitly.
   ENV['RCT_REMOVE_LEGACY_ARCH'] = ENV['RCT_REMOVE_LEGACY_ARCH'] == '0' ? '0' : '1'
@@ -164,6 +170,9 @@ def use_react_native! (
   rncore_pod 'RCTRequired', :path => "#{prefix}/Libraries/Required"
   pod 'RCTTypeSafety', :path => "#{prefix}/Libraries/TypeSafety", :modular_headers => true
   pod 'React', :path => "#{prefix}/"
+  if ENV['RCT_USE_KMP'] == '1'
+    pod 'React-KMP', :path => "#{prefix}/ReactShared"
+  end
   if !ReactNativeCoreUtils.build_rncore_from_source()
     pod 'React-Core-prebuilt', :podspec => "#{prefix}/React-Core-prebuilt.podspec", :modular_headers => true
   end
@@ -632,6 +641,7 @@ def react_native_post_install(
   ReactNativePodsUtils.updateOSDeploymentTarget(installer)
   ReactNativePodsUtils.set_dynamic_frameworks_flags(installer)
   ReactNativePodsUtils.add_ndebug_flag_to_pods_in_release(installer)
+  ReactNativeKMPUtils.configure_aggregate_xcconfig(installer)
 
   if !ReactNativeCoreUtils.build_rncore_from_source()
     # The Xcode-26 SWIFT_ENABLE_EXPLICIT_MODULES=NO workaround (#53457) is removed:
diff --git a/packages/react-native/settings.gradle.kts b/packages/react-native/settings.gradle.kts
index 15a03c394345..61d6d86c5d12 100644
--- a/packages/react-native/settings.gradle.kts
+++ b/packages/react-native/settings.gradle.kts
@@ -21,6 +21,8 @@ pluginManagement {
 
 rootProject.name = "react-native-build-from-source"
 
+includeBuild("ReactShared") { name = "react-native-shared" }
+
 include(":packages:react-native:ReactAndroid")
 
 project(":packages:react-native:ReactAndroid").projectDir = file("ReactAndroid/")
diff --git a/packages/rn-tester/RCTTest/React-RCTTest.podspec b/packages/rn-tester/RCTTest/React-RCTTest.podspec
index e96768635781..b662ace742b5 100644
--- a/packages/rn-tester/RCTTest/React-RCTTest.podspec
+++ b/packages/rn-tester/RCTTest/React-RCTTest.podspec
@@ -38,8 +38,10 @@ Pod::Spec.new do |s|
   s.dependency "React-Core", version
   s.dependency "React-CoreModules", version
   s.dependency "ReactCommon/turbomodule/core", version
+  s.dependency "React-NativeModulesApple", version
   s.dependency "React-jsi", version
 
+  depend_on_js_engine(s)
   add_rn_third_party_dependencies(s)
   add_rncore_dependency(s)
 end
diff --git a/packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m b/packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m
index 4e711d03f56e..84688e4fdaf5 100644
--- a/packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m
+++ b/packages/rn-tester/RNTesterUnitTests/RCTMultipartStreamReaderTests.m
@@ -9,6 +9,44 @@
 
 #import <React/RCTMultipartStreamReader.h>
 
+@interface RCTMultipartFragmentedInputStream : NSInputStream
+- (instancetype)initWithData:(NSData *)data readSize:(NSUInteger)readSize;
+@end
+
+@implementation RCTMultipartFragmentedInputStream {
+  NSData *_data;
+  NSUInteger _offset;
+  NSUInteger _readSize;
+}
+
+- (instancetype)initWithData:(NSData *)data readSize:(NSUInteger)readSize
+{
+  if (self = [super init]) {
+    _data = data;
+    _readSize = readSize;
+  }
+  return self;
+}
+
+- (void)open
+{
+}
+
+- (NSError *)streamError
+{
+  return nil;
+}
+
+- (NSInteger)read:(uint8_t *)buffer maxLength:(NSUInteger)length
+{
+  NSUInteger count = MIN(MIN(length, _readSize), _data.length - _offset);
+  [_data getBytes:buffer range:NSMakeRange(_offset, count)];
+  _offset += count;
+  return count;
+}
+
+@end
+
 @interface RCTMultipartStreamReaderTests : XCTestCase
 
 @end
@@ -115,4 +153,76 @@ - (void)testNoCloseDelimiter
   XCTAssertEqual(count, 1);
 }
 
+- (void)testDelimitersAcrossEveryReadBoundary
+{
+  NSString *body = @"binary\0\r\n--samplX\r\n--sample-\r\n";
+  NSString *response =
+      [NSString stringWithFormat:@"preamble\r\n--sample\r\n%@\r\n--sample\r\nsecond\r\n--sample--\r\nepilogue", body];
+  NSData *data = [response dataUsingEncoding:NSUTF8StringEncoding];
+  for (NSUInteger readSize = 1; readSize <= data.length; readSize++) {
+    NSInputStream *stream = [[RCTMultipartFragmentedInputStream alloc] initWithData:data readSize:readSize];
+    RCTMultipartStreamReader *reader = [[RCTMultipartStreamReader alloc] initWithInputStream:stream boundary:@"sample"];
+    NSMutableArray *parts = [NSMutableArray new];
+    NSMutableArray *last = [NSMutableArray new];
+    BOOL success = [reader
+        readAllPartsWithCompletionCallback:^(__unused NSDictionary *headers, NSData *content, BOOL done) {
+          [parts addObject:content];
+          [last addObject:@(done)];
+        }
+                          progressCallback:nil];
+    XCTAssertTrue(success, @"read size %lu", (unsigned long)readSize);
+    XCTAssertEqualObjects(
+        parts,
+        (@[ [body dataUsingEncoding:NSUTF8StringEncoding], [@"second" dataUsingEncoding:NSUTF8StringEncoding] ]));
+    XCTAssertEqualObjects(last, (@[ @NO, @YES ]));
+  }
+}
+
+- (void)testHeaderWhitespaceDuplicatesAndColonValues
+{
+  NSString *response =
+      @"\r\n--sample\r\n X-Name : first\r\nx-name: second:extra \r\nx-name: last:extra \r\ninvalid\r\n\r\nbody\r\n--sample--\r\n";
+  NSInputStream *stream = [NSInputStream inputStreamWithData:[response dataUsingEncoding:NSUTF8StringEncoding]];
+  RCTMultipartStreamReader *reader = [[RCTMultipartStreamReader alloc] initWithInputStream:stream boundary:@"sample"];
+  __block NSUInteger calls = 0;
+  BOOL success = [reader
+      readAllPartsWithCompletionCallback:^(NSDictionary *headers, NSData *content, BOOL done) {
+        calls++;
+        // Apple keeps header names verbatim and only trims values.
+        XCTAssertEqualObjects(headers, (@{@" X-Name " : @"first", @"x-name" : @"last:extra"}));
+        XCTAssertEqualObjects(content, [@"body" dataUsingEncoding:NSUTF8StringEncoding]);
+        XCTAssertTrue(done);
+      }
+                        progressCallback:nil];
+  XCTAssertTrue(success);
+  XCTAssertEqual(calls, 1);
+}
+
+- (void)testFinalProgressForFragmentedBody
+{
+  NSString *body = [@"" stringByPaddingToLength:64 * 1024 withString:@"x" startingAtIndex:0];
+  NSString *response = [NSString stringWithFormat:@"\r\n--sample\r\nContent-Length: %lu\r\n\r\n%@\r\n--sample--\r\n",
+                                                  (unsigned long)body.length,
+                                                  body];
+  NSInputStream *stream = [NSInputStream inputStreamWithData:[response dataUsingEncoding:NSUTF8StringEncoding]];
+  RCTMultipartStreamReader *reader = [[RCTMultipartStreamReader alloc] initWithInputStream:stream boundary:@"sample"];
+  __block NSUInteger calls = 0;
+  __block NSNumber *lastLength;
+  __block NSNumber *lastLoaded;
+  BOOL success = [reader
+      readAllPartsWithCompletionCallback:^(
+          __unused NSDictionary *headers, __unused NSData *content, __unused BOOL done) {
+        calls++;
+      }
+      progressCallback:^(__unused NSDictionary *headers, NSNumber *length, NSNumber *loaded) {
+        lastLength = length;
+        lastLoaded = loaded;
+      }];
+  XCTAssertTrue(success);
+  XCTAssertEqual(calls, 1);
+  XCTAssertEqualObjects(lastLength, @(body.length));
+  // Preserve Apple's existing progress accounting, including the header/body separator.
+  XCTAssertEqualObjects(lastLoaded, @(body.length + 4));
+}
+
 @end
diff --git a/settings.gradle.kts b/settings.gradle.kts
index 702a042a1088..f93a0eb604b8 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -25,6 +25,8 @@ include(
 
 includeBuild("packages/gradle-plugin/")
 
+includeBuild("packages/react-native/ReactShared") { name = "react-native-shared" }
+
 dependencyResolutionManagement {
   versionCatalogs {
     create("libs") { from(files("packages/react-native/gradle/libs.versions.toml")) }