diff --git a/google/genai/_api_client.py b/google/genai/_api_client.py
index 6fd98c1ce..4ceb255dd 100644
--- a/google/genai/_api_client.py
+++ b/google/genai/_api_client.py
@@ -858,7 +858,7 @@ def _use_google_auth_sync(self) -> bool:
 
   def _use_google_auth_async(self) -> bool:
     try:
-      from google.auth.aio.credentials import StaticCredentials
+      from google.auth.aio.credentials import Credentials as AsyncCredentials
       from google.auth.aio.transport.sessions import AsyncAuthorizedSession
     except ImportError:
       return False
@@ -877,11 +877,36 @@ async def _get_aiohttp_session(
 
     if self._aiohttp_session is None and self._use_google_auth_async():
       try:
-        from google.auth.aio.credentials import StaticCredentials
+        from google.auth.aio.credentials import Credentials as AsyncCredentials
         from google.auth.aio.transport.sessions import AsyncAuthorizedSession
 
-        async_creds = StaticCredentials(token=self._access_token())  # type: ignore[no-untyped-call]
-        self._aiohttp_session = AsyncAuthorizedSession(async_creds)  # type: ignore[no-untyped-call,assignment]
+        class _RefreshableAsyncCredentials(AsyncCredentials):  # type: ignore[misc, valid-type]
+          """Adapter to use the client's sync credentials in an AsyncAuthorizedSession."""
+
+          def __init__(self, client: 'BaseApiClient'):
+            super().__init__()  # type: ignore[no-untyped-call]
+            self._client = client
+
+          async def before_request(
+              self, request: Any, method: str, url: str, headers: dict[str, str]
+          ) -> None:
+            token = await self._client._async_access_token()
+            headers['Authorization'] = f'Bearer {token}'
+            if (
+                self._client._credentials
+                and self._client._credentials.quota_project_id
+            ):
+              headers['x-goog-user-project'] = (
+                  self._client._credentials.quota_project_id
+              )
+
+          @property
+          def valid(self) -> bool:
+            if not self._client._credentials:
+              return False
+            return not self._client._credentials.expired
+
+        self._aiohttp_session = AsyncAuthorizedSession(_RefreshableAsyncCredentials(self))  # type: ignore[no-untyped-call,assignment]
         return self._aiohttp_session  # type: ignore[return-value]
       except ImportError:
         pass