diff --git a/src/google/adk/models/llm_request.py b/src/google/adk/models/llm_request.py
index dcb616bd..79770182 100644
--- a/src/google/adk/models/llm_request.py
+++ b/src/google/adk/models/llm_request.py
@@ -45,7 +45,9 @@ class LlmRequest(BaseModel):
   contents: list[types.Content] = Field(default_factory=list)
   """The contents to send to the model."""
 
-  config: Optional[types.GenerateContentConfig] = None
+  config: types.GenerateContentConfig = Field(
+      default_factory=types.GenerateContentConfig
+  )
   live_connect_config: types.LiveConnectConfig = types.LiveConnectConfig()
   """Additional config for the generate content request.
 
diff --git a/tests/unittests/models/test_google_llm.py b/tests/unittests/models/test_google_llm.py
index 03d18ec6..9004245c 100644
--- a/tests/unittests/models/test_google_llm.py
+++ b/tests/unittests/models/test_google_llm.py
@@ -1505,7 +1505,6 @@ async def test_computer_use_with_no_config():
       contents=[
           types.Content(role="user", parts=[types.Part.from_text(text="Hello")])
       ],
-      config=None,
   )
 
   # Should not raise an exception
diff --git a/tests/unittests/tools/test_base_tool.py b/tests/unittests/tools/test_base_tool.py
index d450cc0e..da1dda64 100644
--- a/tests/unittests/tools/test_base_tool.py
+++ b/tests/unittests/tools/test_base_tool.py
@@ -62,7 +62,7 @@ async def test_process_llm_request_no_declaration():
       tool_context=tool_context, llm_request=llm_request
   )
 
-  assert llm_request.config is None
+  assert llm_request.config == types.GenerateContentConfig()
 
 
 @pytest.mark.asyncio
diff --git a/tests/unittests/tools/test_google_search_tool.py b/tests/unittests/tools/test_google_search_tool.py
index c297e438..9623875a 100644
--- a/tests/unittests/tools/test_google_search_tool.py
+++ b/tests/unittests/tools/test_google_search_tool.py
@@ -322,12 +322,12 @@ class TestGoogleSearchTool:
       )
 
   @pytest.mark.asyncio
-  async def test_process_llm_request_with_none_config(self):
+  async def test_process_llm_request_with_no_config(self):
     """Test processing LLM request with None config."""
     tool = GoogleSearchTool()
     tool_context = await _create_tool_context()
 
-    llm_request = LlmRequest(model='gemini-2.0-flash', config=None)
+    llm_request = LlmRequest(model='gemini-2.0-flash')
 
     await tool.process_llm_request(
         tool_context=tool_context, llm_request=llm_request
diff --git a/tests/unittests/tools/test_url_context_tool.py b/tests/unittests/tools/test_url_context_tool.py
index e4c53302..cbbbb0c9 100644
--- a/tests/unittests/tools/test_url_context_tool.py
+++ b/tests/unittests/tools/test_url_context_tool.py
@@ -242,12 +242,12 @@ class TestUrlContextTool:
       )
 
   @pytest.mark.asyncio
-  async def test_process_llm_request_with_none_config(self):
+  async def test_process_llm_request_with_no_config(self):
     """Test processing LLM request with None config."""
     tool = UrlContextTool()
     tool_context = await _create_tool_context()
 
-    llm_request = LlmRequest(model='gemini-2.0-flash', config=None)
+    llm_request = LlmRequest(model='gemini-2.0-flash')
 
     await tool.process_llm_request(
         tool_context=tool_context, llm_request=llm_request