diff --git a/contributing/samples/gepa/experiment.py b/contributing/samples/gepa/experiment.py
index 2f5d03a772..f68b349d9c 100644
--- a/contributing/samples/gepa/experiment.py
+++ b/contributing/samples/gepa/experiment.py
@@ -43,7 +43,6 @@
 from tau_bench.types import EnvRunResult
 from tau_bench.types import RunConfig
 import tau_bench_agent as tau_bench_agent_lib
-
 import utils
 
 
diff --git a/contributing/samples/gepa/run_experiment.py b/contributing/samples/gepa/run_experiment.py
index cfd850b3a3..1bc4ee58c8 100644
--- a/contributing/samples/gepa/run_experiment.py
+++ b/contributing/samples/gepa/run_experiment.py
@@ -25,7 +25,6 @@
 from absl import flags
 import experiment
 from google.genai import types
-
 import utils
 
 _OUTPUT_DIR = flags.DEFINE_string(
diff --git a/src/google/adk/models/google_llm.py b/src/google/adk/models/google_llm.py
index 6b21cf62c7..7dc413242f 100644
--- a/src/google/adk/models/google_llm.py
+++ b/src/google/adk/models/google_llm.py
@@ -25,6 +25,7 @@
 from typing import TYPE_CHECKING
 from typing import Union
 
+import google.auth.credentials
 from google.genai import types
 from google.genai.errors import ClientError
 from typing_extensions import override
@@ -87,6 +88,12 @@ class Gemini(BaseLlm):
 
   model: str = 'gemini-2.5-flash'
 
+  vertexai: Optional[bool] = None
+  api_key: Optional[str] = None
+  credentials: Optional[google.auth.credentials.Credentials] = None
+  project: Optional[str] = None
+  location: Optional[str] = None
+
   speech_config: Optional[types.SpeechConfig] = None
 
   retry_options: Optional[types.HttpRetryOptions] = None
@@ -241,10 +248,15 @@ def api_client(self) -> Client:
     from google.genai import Client
 
     return Client(
+        vertexai=self.vertexai,
+        api_key=self.api_key,
+        credentials=self.credentials,
+        project=self.project,
+        location=self.location,
         http_options=types.HttpOptions(
             headers=self._tracking_headers(),
             retry_options=self.retry_options,
-        )
+        ),
     )
 
   @cached_property
@@ -278,9 +290,14 @@ def _live_api_client(self) -> Client:
     from google.genai import Client
 
     return Client(
+        vertexai=self.vertexai,
+        api_key=self.api_key,
+        credentials=self.credentials,
+        project=self.project,
+        location=self.location,
         http_options=types.HttpOptions(
             headers=self._tracking_headers(), api_version=self._live_api_version
-        )
+        ),
     )
 
   @contextlib.asynccontextmanager