diff --git a/src/google/adk/evaluation/local_eval_service.py b/src/google/adk/evaluation/local_eval_service.py
index fa50f70d..f443bb70 100644
--- a/src/google/adk/evaluation/local_eval_service.py
+++ b/src/google/adk/evaluation/local_eval_service.py
@@ -68,19 +68,14 @@ class LocalEvalService(BaseEvalService):
       self,
       root_agent: BaseAgent,
       eval_sets_manager: EvalSetsManager,
-      metric_evaluator_registry: Optional[MetricEvaluatorRegistry] = None,
-      session_service: Optional[BaseSessionService] = None,
-      artifact_service: Optional[BaseArtifactService] = None,
+      metric_evaluator_registry: MetricEvaluatorRegistry = DEFAULT_METRIC_EVALUATOR_REGISTRY,
+      session_service: BaseSessionService = InMemorySessionService(),
+      artifact_service: BaseArtifactService = InMemoryArtifactService(),
       eval_set_results_manager: Optional[EvalSetResultsManager] = None,
       session_id_supplier: Callable[[], str] = _get_session_id,
   ):
     self._root_agent = root_agent
     self._eval_sets_manager = eval_sets_manager
-    metric_evaluator_registry = (
-        metric_evaluator_registry or DEFAULT_METRIC_EVALUATOR_REGISTRY
-    )
-    session_service = session_service or InMemorySessionService()
-    artifact_service = artifact_service or InMemoryArtifactService()
     self._metric_evaluator_registry = metric_evaluator_registry
     self._session_service = session_service
     self._artifact_service = artifact_service
diff --git a/src/google/adk/runners.py b/src/google/adk/runners.py
index d18127b1..f0f92047 100644
--- a/src/google/adk/runners.py
+++ b/src/google/adk/runners.py
@@ -188,7 +188,7 @@ class Runner:
       user_id: str,
       session_id: str,
       new_message: types.Content,
-      run_config: Optional[RunConfig] = None,
+      run_config: RunConfig = RunConfig(),
   ) -> Generator[Event, None, None]:
     """Runs the agent.
 
@@ -205,7 +205,6 @@ class Runner:
     Yields:
       The events generated by the agent.
     """
-    run_config = run_config or RunConfig()
     event_queue = queue.Queue()
 
     async def _invoke_run_async():
@@ -249,7 +248,7 @@ class Runner:
       session_id: str,
       new_message: types.Content,
       state_delta: Optional[dict[str, Any]] = None,
-      run_config: Optional[RunConfig] = None,
+      run_config: RunConfig = RunConfig(),
   ) -> AsyncGenerator[Event, None]:
     """Main entry method to run the agent in this runner.
 
@@ -262,7 +261,6 @@ class Runner:
     Yields:
       The events generated by the agent.
     """
-    run_config = run_config or RunConfig()
 
     async def _run_with_trace(
         new_message: types.Content,
@@ -428,7 +426,7 @@ class Runner:
       user_id: Optional[str] = None,
       session_id: Optional[str] = None,
       live_request_queue: LiveRequestQueue,
-      run_config: Optional[RunConfig] = None,
+      run_config: RunConfig = RunConfig(),
       session: Optional[Session] = None,
   ) -> AsyncGenerator[Event, None]:
     """Runs the agent in live mode (experimental feature).
@@ -454,7 +452,6 @@ class Runner:
     .. NOTE::
         Either `session` or both `user_id` and `session_id` must be provided.
     """
-    run_config = run_config or RunConfig()
     if session is None and (user_id is None or session_id is None):
       raise ValueError(
           'Either session or user_id and session_id must be provided.'
@@ -604,7 +601,7 @@ class Runner:
       *,
       new_message: Optional[types.Content] = None,
       live_request_queue: Optional[LiveRequestQueue] = None,
-      run_config: Optional[RunConfig] = None,
+      run_config: RunConfig = RunConfig(),
   ) -> InvocationContext:
     """Creates a new invocation context.
 
@@ -617,7 +614,6 @@ class Runner:
     Returns:
         The new invocation context.
     """
-    run_config = run_config or RunConfig()
     invocation_id = new_invocation_context_id()
 
     if run_config.support_cfc and isinstance(self.agent, LlmAgent):
@@ -649,10 +645,9 @@ class Runner:
       session: Session,
       *,
       live_request_queue: Optional[LiveRequestQueue] = None,
-      run_config: Optional[RunConfig] = None,
+      run_config: RunConfig = RunConfig(),
   ) -> InvocationContext:
     """Creates a new invocation context for live multi-agent."""
-    run_config = run_config or RunConfig()
 
     # For live multi-agent, we need model's text transcription as context for
     # next agent.
diff --git a/tests/unittests/cli/test_fast_api.py b/tests/unittests/cli/test_fast_api.py
index d0d84cac..b05bf3c4 100755
--- a/tests/unittests/cli/test_fast_api.py
+++ b/tests/unittests/cli/test_fast_api.py
@@ -21,7 +21,6 @@ import sys
 import tempfile
 import time
 from typing import Any
-from typing import Optional
 from unittest.mock import MagicMock
 from unittest.mock import patch
 
@@ -121,9 +120,8 @@ async def dummy_run_async(
     session_id,
     new_message,
     state_delta=None,
-    run_config: Optional[RunConfig] = None,
+    run_config: RunConfig = RunConfig(),
 ):
-  run_config = run_config or RunConfig()
   yield _event_1()
   await asyncio.sleep(0)