diff --git a/src/google/adk/models/apigee_llm.py b/src/google/adk/models/apigee_llm.py
index 65c4156744..2667ae8e00 100644
--- a/src/google/adk/models/apigee_llm.py
+++ b/src/google/adk/models/apigee_llm.py
@@ -40,6 +40,7 @@
 from .llm_response import LlmResponse
 
 if TYPE_CHECKING:
+  from google.auth.credentials import Credentials
   from google.genai import Client
 
   from .llm_request import LlmRequest
@@ -92,6 +93,7 @@ def __init__(
       custom_headers: dict[str, str] | None = None,
       retry_options: Optional[types.HttpRetryOptions] = None,
       api_type: ApiType | str = ApiType.UNKNOWN,
+      credentials: Optional[Credentials] = None,
   ):
     """Initializes the Apigee LLM backend.
 
@@ -123,6 +125,11 @@ def __init__(
         authorization headers in Vertex AI and Gemini API calls.
       retry_options: Allow google-genai to retry failed responses.
       api_type: The type of API to use. One of `ApiType` or string.
+      credentials: Optional google-auth credentials passed through to the
+        underlying `genai.Client`. Use this when the Apigee proxy requires
+        additional OAuth scopes (e.g., `userinfo.email` for tokeninfo-based
+        caller identification). When omitted, the default `genai.Client`
+        authentication flow is used.
     """  # fmt: skip
 
     super().__init__(model=model, retry_options=retry_options)
@@ -165,6 +172,7 @@ def __init__(
     )
     self._custom_headers = custom_headers or {}
     self._user_agent = f'google-adk/{adk_version.__version__}'
+    self._credentials = credentials
 
   @classmethod
   @override
@@ -239,6 +247,8 @@ def api_client(self) -> Client:
     if self._isvertexai:
       kwargs_for_client['project'] = self._project
       kwargs_for_client['location'] = self._location
+    if self._credentials is not None:
+      kwargs_for_client['credentials'] = self._credentials
 
     return Client(
         http_options=http_options,
diff --git a/tests/unittests/models/test_apigee_llm.py b/tests/unittests/models/test_apigee_llm.py
index ecbb61d18f..1e371e8aa1 100644
--- a/tests/unittests/models/test_apigee_llm.py
+++ b/tests/unittests/models/test_apigee_llm.py
@@ -651,6 +651,71 @@ def test_parse_response_usage_metadata():
   assert llm_response.usage_metadata.thoughts_token_count == 4
 
 
+@pytest.mark.asyncio
+@mock.patch('google.genai.Client')
+async def test_api_client_passes_credentials_when_provided(
+    mock_client_constructor, llm_request
+):
+  """Tests that credentials passed to __init__ are forwarded to genai.Client."""
+  mock_credentials = mock.Mock()
+
+  mock_client_instance = mock.Mock()
+  mock_client_instance.aio.models.generate_content = AsyncMock(
+      return_value=types.GenerateContentResponse(
+          candidates=[
+              types.Candidate(
+                  content=Content(
+                      parts=[Part.from_text(text='Test response')],
+                      role='model',
+                  )
+              )
+          ]
+      )
+  )
+  mock_client_constructor.return_value = mock_client_instance
+
+  apigee_llm = ApigeeLlm(
+      model=APIGEE_GEMINI_MODEL_ID,
+      proxy_url=PROXY_URL,
+      credentials=mock_credentials,
+  )
+  _ = [resp async for resp in apigee_llm.generate_content_async(llm_request)]
+
+  _, kwargs = mock_client_constructor.call_args
+  assert kwargs['credentials'] is mock_credentials
+
+
+@pytest.mark.asyncio
+@mock.patch('google.genai.Client')
+async def test_api_client_omits_credentials_when_not_provided(
+    mock_client_constructor, llm_request
+):
+  """Tests that credentials kwarg is not forwarded when not supplied."""
+  mock_client_instance = mock.Mock()
+  mock_client_instance.aio.models.generate_content = AsyncMock(
+      return_value=types.GenerateContentResponse(
+          candidates=[
+              types.Candidate(
+                  content=Content(
+                      parts=[Part.from_text(text='Test response')],
+                      role='model',
+                  )
+              )
+          ]
+      )
+  )
+  mock_client_constructor.return_value = mock_client_instance
+
+  apigee_llm = ApigeeLlm(
+      model=APIGEE_GEMINI_MODEL_ID,
+      proxy_url=PROXY_URL,
+  )
+  _ = [resp async for resp in apigee_llm.generate_content_async(llm_request)]
+
+  _, kwargs = mock_client_constructor.call_args
+  assert 'credentials' not in kwargs
+
+
 def test_parse_response_with_refusal():
   """Tests that CompletionsHTTPClient parses refusal correctly."""
   client = CompletionsHTTPClient(base_url='http://test')