diff --git a/.changeset/fix-standard-schema-dependency.md b/.changeset/fix-standard-schema-dependency.md
new file mode 100644
index 00000000..c85d1370
--- /dev/null
+++ b/.changeset/fix-standard-schema-dependency.md
@@ -0,0 +1,7 @@
+---
+'@tanstack/ai': patch
+---
+
+fix(ai): move @standard-schema/spec from devDependencies to dependencies
+
+Without this package installed, all types that depend on `StandardJSONSchemaV1` silently degrade to `any` — tool definitions lose type inference and `chat()` return types become `any`.
diff --git a/packages/typescript/ai/package.json b/packages/typescript/ai/package.json
index 2f483b78..9d8b9224 100644
--- a/packages/typescript/ai/package.json
+++ b/packages/typescript/ai/package.json
@@ -57,11 +57,11 @@
     "tanstack-intent"
   ],
   "dependencies": {
+    "@standard-schema/spec": "^1.1.0",
     "@tanstack/ai-event-client": "workspace:*",
     "partial-json": "^0.1.7"
   },
   "devDependencies": {
-    "@standard-schema/spec": "^1.1.0",
     "@vitest/coverage-v8": "4.0.14",
     "zod": "^4.2.0"
   }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 7e13a402..af65e870 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -807,6 +807,9 @@ importers:
 
   packages/typescript/ai:
     dependencies:
+      '@standard-schema/spec':
+        specifier: ^1.1.0
+        version: 1.1.0
       '@tanstack/ai-event-client':
         specifier: workspace:*
         version: link:../ai-event-client
@@ -814,9 +817,6 @@ importers:
         specifier: ^0.1.7
         version: 0.1.7
     devDependencies:
-      '@standard-schema/spec':
-        specifier: ^1.1.0
-        version: 1.1.0
       '@vitest/coverage-v8':
         specifier: 4.0.14
         version: 4.0.14(vitest@4.1.4)