diff --git a/src/google/adk/tools/google_search_tool.py b/src/google/adk/tools/google_search_tool.py
index 8d73ced8d2..f8d9f0491f 100644
--- a/src/google/adk/tools/google_search_tool.py
+++ b/src/google/adk/tools/google_search_tool.py
@@ -35,17 +35,26 @@ class GoogleSearchTool(BaseTool):
   local code execution.
   """
 
-  def __init__(self, *, bypass_multi_tools_limit: bool = False):
+  def __init__(
+      self,
+      *,
+      bypass_multi_tools_limit: bool = False,
+      model: str | None = None,
+  ):
     """Initializes the Google search tool.
 
     Args:
       bypass_multi_tools_limit: Whether to bypass the multi tools limitation,
         so that the tool can be used with other tools in the same agent.
+      model: Optional model name to use for processing the LLM request. If
+        provided, this model will be used instead of the model from the
+        incoming llm_request.
     """
 
     # Name and description are not used because this is a model built-in tool.
     super().__init__(name='google_search', description='google_search')
     self.bypass_multi_tools_limit = bypass_multi_tools_limit
+    self.model = model
 
   @override
   async def process_llm_request(
@@ -54,6 +63,10 @@ async def process_llm_request(
       tool_context: ToolContext,
       llm_request: LlmRequest,
   ) -> None:
+    # If a custom model is specified, use it instead of the original model
+    if self.model is not None:
+      llm_request.model = self.model
+
     llm_request.config = llm_request.config or types.GenerateContentConfig()
     llm_request.config.tools = llm_request.config.tools or []
     if is_gemini_1_model(llm_request.model):
diff --git a/tests/unittests/tools/test_google_search_tool.py b/tests/unittests/tools/test_google_search_tool.py
index 2f090abb17..8266f6e0d6 100644
--- a/tests/unittests/tools/test_google_search_tool.py
+++ b/tests/unittests/tools/test_google_search_tool.py
@@ -432,3 +432,46 @@ async def test_process_llm_request_gemini_version_specifics(self):
       assert len(llm_request.config.tools) == 1
       assert llm_request.config.tools[0].google_search is not None
       assert llm_request.config.tools[0].google_search_retrieval is None
+
+  @pytest.mark.asyncio
+  @pytest.mark.parametrize(
+      (
+          'tool_model',
+          'request_model',
+          'expected_model',
+      ),
+      [
+          (
+              'gemini-2.5-flash-lite',
+              'gemini-2.5-flash',
+              'gemini-2.5-flash-lite',
+          ),
+          (
+              None,
+              'gemini-2.5-flash',
+              'gemini-2.5-flash',
+          ),
+      ],
+      ids=['with_custom_model', 'without_custom_model'],
+  )
+  async def test_process_llm_request_custom_model_behavior(
+      self,
+      tool_model,
+      request_model,
+      expected_model,
+  ):
+    """Tests custom model parameter behavior in process_llm_request."""
+    tool = GoogleSearchTool(model=tool_model)
+    tool_context = await _create_tool_context()
+
+    llm_request = LlmRequest(
+        model=request_model, config=types.GenerateContentConfig()
+    )
+
+    await tool.process_llm_request(
+        tool_context=tool_context, llm_request=llm_request
+    )
+
+    assert llm_request.model == expected_model
+    assert llm_request.config.tools is not None
+    assert len(llm_request.config.tools) == 1