diff --git a/contributing/samples/built_in_multi_tools/agent.py b/contributing/samples/built_in_multi_tools/agent.py
index 5194e0ef..3eb9ce8b 100644
--- a/contributing/samples/built_in_multi_tools/agent.py
+++ b/contributing/samples/built_in_multi_tools/agent.py
@@ -17,7 +17,7 @@ import random
 
 from dotenv import load_dotenv
 from google.adk import Agent
-from google.adk.tools.google_search_tool import google_search
+from google.adk.tools.google_search_tool import GoogleSearchTool
 from google.adk.tools.tool_context import ToolContext
 from google.adk.tools.vertex_ai_search_tool import VertexAiSearchTool
 
@@ -57,7 +57,9 @@ root_agent = Agent(
     """,
     tools=[
         roll_die,
-        VertexAiSearchTool(data_store_id=VERTEXAI_DATASTORE_ID),
-        google_search,
+        VertexAiSearchTool(
+            data_store_id=VERTEXAI_DATASTORE_ID, bypass_multi_tools_limit=True
+        ),
+        GoogleSearchTool(bypass_multi_tools_limit=True),
     ],
 )
diff --git a/src/google/adk/flows/llm_flows/base_llm_flow.py b/src/google/adk/flows/llm_flows/base_llm_flow.py
index f5b242b7..531a5034 100644
--- a/src/google/adk/flows/llm_flows/base_llm_flow.py
+++ b/src/google/adk/flows/llm_flows/base_llm_flow.py
@@ -438,6 +438,10 @@ class BaseLlmFlow(ABC):
     from ...agents.llm_agent import LlmAgent
 
     agent = invocation_context.agent
+    if not isinstance(agent, LlmAgent):
+      raise TypeError(
+          f'Expected agent to be an LlmAgent, but got {type(agent)}'
+      )
 
     # Runs processors.
     for processor in self.request_processors:
@@ -468,7 +472,7 @@ class BaseLlmFlow(ABC):
       tools = await _convert_tool_union_to_tools(
           tool_union,
           ReadonlyContext(invocation_context),
-          llm_request.model,
+          agent.model,
           multiple_tools,
       )
       for tool in tools:
diff --git a/tests/unittests/flows/llm_flows/test_base_llm_flow.py b/tests/unittests/flows/llm_flows/test_base_llm_flow.py
index 47b4b00f..81ef925a 100644
--- a/tests/unittests/flows/llm_flows/test_base_llm_flow.py
+++ b/tests/unittests/flows/llm_flows/test_base_llm_flow.py
@@ -14,13 +14,13 @@
 
 """Unit tests for BaseLlmFlow toolset integration."""
 
-from typing import Optional
+from unittest import mock
 from unittest.mock import AsyncMock
 
-from google.adk.agents.callback_context import CallbackContext
 from google.adk.agents.llm_agent import Agent
 from google.adk.events.event import Event
 from google.adk.flows.llm_flows.base_llm_flow import BaseLlmFlow
+from google.adk.models.google_llm import Gemini
 from google.adk.models.llm_request import LlmRequest
 from google.adk.models.llm_response import LlmResponse
 from google.adk.plugins.base_plugin import BasePlugin
@@ -95,7 +95,6 @@ async def test_preprocess_calls_toolset_process_llm_request():
 async def test_preprocess_handles_mixed_tools_and_toolsets():
   """Test that _preprocess_async properly handles both tools and toolsets."""
   from google.adk.tools.base_tool import BaseTool
-  from google.adk.tools.function_tool import FunctionTool
 
   # Create a mock tool
   class _MockTool(BaseTool):
@@ -200,6 +199,46 @@ async def test_preprocess_with_google_search_workaround():
   assert {d.name for d in declarations} == {'_my_tool', 'google_search_agent'}
 
 
+@pytest.mark.asyncio
+async def test_preprocess_calls_convert_tool_union_to_tools():
+  """Test that _preprocess_async calls _convert_tool_union_to_tools."""
+
+  class _MockTool:
+    process_llm_request = AsyncMock()
+
+  mock_tool_instance = _MockTool()
+
+  def _my_tool(sides: int) -> int:
+    """A simple tool."""
+    return sides
+
+  with mock.patch(
+      'google.adk.agents.llm_agent._convert_tool_union_to_tools',
+      new_callable=AsyncMock,
+  ) as mock_convert:
+    mock_convert.return_value = [mock_tool_instance]
+
+    model = Gemini(model='gemini-2')
+    agent = Agent(
+        name='test_agent', model=model, tools=[_my_tool, google_search]
+    )
+    invocation_context = await testing_utils.create_invocation_context(
+        agent=agent, user_content='test message'
+    )
+    flow = BaseLlmFlowForTesting()
+    llm_request = LlmRequest(model='gemini-2')
+
+    async for _ in flow._preprocess_async(invocation_context, llm_request):
+      pass
+
+    mock_convert.assert_called_with(
+        google_search,
+        mock.ANY,  # ReadonlyContext(invocation_context)
+        model,
+        True,  # multiple_tools
+    )
+
+
 # TODO(b/448114567): Remove the following
 # test_handle_after_model_callback_grounding tests once the workaround
 # is no longer needed.