diff --git a/packages/google-auth/google/auth/transport/grpc.py b/packages/google-auth/google/auth/transport/grpc.py
index 7482038589a3..d2165df0ab39 100644
--- a/packages/google-auth/google/auth/transport/grpc.py
+++ b/packages/google-auth/google/auth/transport/grpc.py
@@ -17,6 +17,7 @@
 from __future__ import absolute_import
 
 import logging
+from typing import Set
 
 from google.auth import exceptions
 from google.auth.transport import _mtls_helper
@@ -32,6 +33,8 @@
 
 _LOGGER = logging.getLogger(__name__)
 
+__lazy_modules__: Set[str] = {"grpc"}
+
 
 class AuthMetadataPlugin(grpc.AuthMetadataPlugin):
     """A `gRPC AuthMetadataPlugin`_ that inserts the credentials into each
diff --git a/packages/google-auth/google/auth/transport/requests.py b/packages/google-auth/google/auth/transport/requests.py
index eef0384652a6..483f3a0b1fe9 100644
--- a/packages/google-auth/google/auth/transport/requests.py
+++ b/packages/google-auth/google/auth/transport/requests.py
@@ -21,7 +21,7 @@
 import logging
 import numbers
 import time
-from typing import Optional
+from typing import Optional, Set
 
 try:
     import requests
@@ -42,6 +42,8 @@
 import google.auth.transport._mtls_helper
 from google.oauth2 import service_account
 
+__lazy_modules__: Set[str] = {"requests", "requests.adapters", "requests.exceptions"}
+
 _LOGGER = logging.getLogger(__name__)
 
 _DEFAULT_TIMEOUT = 120  # in seconds
diff --git a/packages/google-auth/google/auth/transport/urllib3.py b/packages/google-auth/google/auth/transport/urllib3.py
index 1b0fac7c342f..3f56029794d9 100644
--- a/packages/google-auth/google/auth/transport/urllib3.py
+++ b/packages/google-auth/google/auth/transport/urllib3.py
@@ -16,8 +16,10 @@
 
 from __future__ import absolute_import
 
+
 import http.client as http_client
 import logging
+from typing import Set
 import warnings
 
 # Certifi is Mozilla's certificate bundle. Urllib3 needs a certificate bundle
@@ -56,6 +58,14 @@
 from google.auth.transport import _mtls_helper
 from google.oauth2 import service_account
 
+__lazy_modules__: Set[str] = {
+    "urllib3",
+    "urllib3.exceptions",
+    "certifi",
+    "packaging",
+    "packaging.version",
+}
+
 if version.parse(urllib3.__version__) >= version.parse("2.0.0"):  # pragma: NO COVER
     RequestMethods = urllib3._request_methods.RequestMethods  # type: ignore
 else:  # pragma: NO COVER
diff --git a/packages/google-auth/tests/transport/test_lazy_imports.py b/packages/google-auth/tests/transport/test_lazy_imports.py
new file mode 100644
index 000000000000..bd472440e61e
--- /dev/null
+++ b/packages/google-auth/tests/transport/test_lazy_imports.py
@@ -0,0 +1,77 @@
+# Copyright 2026 Google LLC
+#
+# 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
+#
+#      http://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.
+
+import subprocess
+import sys
+
+import pytest
+
+SCRIPT_PYTHON_315 = """
+import sys
+import google.auth.transport.requests
+import google.auth.transport.urllib3
+import google.auth.transport.grpc
+
+# The heavy underlying modules should NOT be loaded yet
+HEAVY_MODULES = ["requests", "urllib3", "grpc"]
+
+for mod in HEAVY_MODULES:
+    if mod in sys.modules:
+        print(f"FAILED: {mod} was eagerly loaded into sys.modules")
+        sys.exit(1)
+
+# Trigger reification
+import requests
+_ = requests.__name__
+
+if "requests" not in sys.modules:
+    print("FAILED: requests was not lazily loaded upon access")
+    sys.exit(2)
+
+sys.exit(0)
+"""
+
+SCRIPT_PRE_315 = """
+import sys
+import google.auth.transport.requests
+import google.auth.transport.urllib3
+import google.auth.transport.grpc
+
+HEAVY_MODULES = ["requests", "urllib3", "grpc"]
+
+for mod in HEAVY_MODULES:
+    if mod not in sys.modules:
+        print(f"FAILED: {mod} was not eagerly loaded into sys.modules")
+        sys.exit(1)
+
+sys.exit(0)
+"""
+
+
+@pytest.mark.skipif(sys.version_info < (3, 15), reason="PEP 810 requires Python 3.15+")
+def test_lazy_imports_on_python_315():
+    result = subprocess.run(
+        [sys.executable, "-c", SCRIPT_PYTHON_315], capture_output=True, text=True
+    )
+    assert result.returncode == 0, f"Subprocess failed: {result.stdout}"
+
+
+@pytest.mark.skipif(
+    sys.version_info >= (3, 15), reason="Testing fallback behavior on < 3.15"
+)
+def test_fallback_eager_imports_pre_315():
+    result = subprocess.run(
+        [sys.executable, "-c", SCRIPT_PRE_315], capture_output=True, text=True
+    )
+    assert result.returncode == 0, f"Subprocess failed: {result.stdout}"