chore: Disable SetModelResponseTool workaround for Vertex AI Gemini 2+ models

Gemini models now [support Function calling being used together with structured output on Vertex AI](https://cloud.google.com/vertex-ai/generative-ai/docs/multimodal/function-calling#structured-output-bp).

Co-authored-by: Xuan Yang <xygoogle@google.com>
PiperOrigin-RevId: 827709903

src/google/adk/flows/llm_flows/_output_schema_processor.py

@@ -25,6 +25,7 @@ from ...agents.invocation_context import InvocationContext
 from ...events.event import Event
 from ...models.llm_request import LlmRequest
 from ...tools.set_model_response_tool import SetModelResponseTool
+from ...utils.output_schema_utils import can_use_output_schema_with_tools
 from ._base_llm_processor import BaseLlmRequestProcessor
 
 
@@ -39,8 +40,13 @@ class _OutputSchemaRequestProcessor(BaseLlmRequestProcessor):
 
     agent = invocation_context.agent
 
-    # Check if we need the processor: output_schema + tools
-    if not agent.output_schema or not agent.tools:
+    # Check if we need the processor: output_schema + tools + cannot use output
+    # schema with tools
+    if (
+        not agent.output_schema
+        or not agent.tools
+        or can_use_output_schema_with_tools(agent.model)
+    ):
       return
 
     # Add the set_model_response tool to handle structured output

src/google/adk/flows/llm_flows/basic.py

@@ -25,6 +25,7 @@ from typing_extensions import override
 from ...agents.invocation_context import InvocationContext
 from ...events.event import Event
 from ...models.llm_request import LlmRequest
+from ...utils.output_schema_utils import can_use_output_schema_with_tools
 from ._base_llm_processor import BaseLlmRequestProcessor
 
 
@@ -52,8 +53,9 @@ class _BasicLlmRequestProcessor(BaseLlmRequestProcessor):
     # support output_schema and tools together. we have a workaround to support
     # both output_schema and tools at the same time. see
     # _output_schema_processor.py for details
-    if agent.output_schema and not agent.tools:
-      llm_request.set_output_schema(agent.output_schema)
+    if agent.output_schema:
+      if not agent.tools or can_use_output_schema_with_tools(agent.model):
+        llm_request.set_output_schema(agent.output_schema)
 
     llm_request.live_connect_config.response_modalities = (
         invocation_context.run_config.response_modalities

src/google/adk/utils/output_schema_utils.py

@@ -0,0 +1,38 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Utilities for Output Schema.
+
+This module is for ADK internal use only.
+Please do not rely on the implementation details.
+"""
+
+from __future__ import annotations
+
+from typing import Union
+
+from ..models.base_llm import BaseLlm
+from .model_name_utils import is_gemini_2_or_above
+from .variant_utils import get_google_llm_variant
+from .variant_utils import GoogleLLMVariant
+
+
+def can_use_output_schema_with_tools(model: Union[str, BaseLlm]):
+  """Returns True if output schema with tools is supported."""
+  model_string = model if isinstance(model, str) else model.model
+
+  return (
+      get_google_llm_variant() == GoogleLLMVariant.VERTEX_AI
+      and is_gemini_2_or_above(model_string)
+  )

tests/unittests/flows/llm_flows/test_basic_processor.py

@@ -14,6 +14,8 @@
 
 """Tests for basic LLM request processor."""
 
+from unittest import mock
+
 from google.adk.agents.invocation_context import InvocationContext
 from google.adk.agents.llm_agent import LlmAgent
 from google.adk.agents.run_config import RunConfig
@@ -80,7 +82,7 @@ class TestBasicLlmRequestProcessor:
     assert llm_request.config.response_mime_type == 'application/json'
 
   @pytest.mark.asyncio
-  async def test_skips_output_schema_when_tools_present(self):
+  async def test_skips_output_schema_when_tools_present(self, mocker):
     """Test that processor skips output_schema when agent has tools."""
     agent = LlmAgent(
         name='test_agent',
@@ -93,6 +95,11 @@ class TestBasicLlmRequestProcessor:
     llm_request = LlmRequest()
     processor = _BasicLlmRequestProcessor()
 
+    can_use_output_schema_with_tools = mocker.patch(
+        'google.adk.flows.llm_flows.basic.can_use_output_schema_with_tools',
+        mock.MagicMock(return_value=False),
+    )
+
     # Process the request
     events = []
     async for event in processor.run_async(invocation_context, llm_request):
@@ -102,6 +109,40 @@ class TestBasicLlmRequestProcessor:
     assert llm_request.config.response_schema is None
     assert llm_request.config.response_mime_type != 'application/json'
 
+    # Should have checked if output schema can be used with tools
+    can_use_output_schema_with_tools.assert_called_once_with(agent.model)
+
+  @pytest.mark.asyncio
+  async def test_sets_output_schema_when_tools_present(self, mocker):
+    """Test that processor skips output_schema when agent has tools."""
+    agent = LlmAgent(
+        name='test_agent',
+        model='gemini-2.5-flash',
+        output_schema=OutputSchema,
+        tools=[FunctionTool(func=dummy_tool)],  # Has tools
+    )
+
+    invocation_context = await _create_invocation_context(agent)
+    llm_request = LlmRequest()
+    processor = _BasicLlmRequestProcessor()
+
+    can_use_output_schema_with_tools = mocker.patch(
+        'google.adk.flows.llm_flows.basic.can_use_output_schema_with_tools',
+        mock.MagicMock(return_value=True),
+    )
+
+    # Process the request
+    events = []
+    async for event in processor.run_async(invocation_context, llm_request):
+      events.append(event)
+
+    # Should have set response_schema since output schema can be used with tools
+    assert llm_request.config.response_schema == OutputSchema
+    assert llm_request.config.response_mime_type == 'application/json'
+
+    # Should have checked if output schema can be used with tools
+    can_use_output_schema_with_tools.assert_called_once_with(agent.model)
+
   @pytest.mark.asyncio
   async def test_no_output_schema_no_tools(self):
     """Test that processor works normally when agent has no output_schema or tools."""

tests/unittests/flows/llm_flows/test_output_schema_processor.py

@@ -14,14 +14,13 @@
 
 """Tests for output schema processor functionality."""
 
-import json
+from unittest import mock
 
 from google.adk.agents.invocation_context import InvocationContext
 from google.adk.agents.llm_agent import LlmAgent
 from google.adk.agents.run_config import RunConfig
 from google.adk.flows.llm_flows.single_flow import SingleFlow
 from google.adk.models.llm_request import LlmRequest
-from google.adk.models.llm_response import LlmResponse
 from google.adk.sessions.in_memory_session_service import InMemorySessionService
 from google.adk.tools.function_tool import FunctionTool
 from pydantic import BaseModel
@@ -145,7 +144,16 @@ async def test_basic_processor_sets_output_schema_without_tools():
 
 
 @pytest.mark.asyncio
-async def test_output_schema_request_processor():
+@pytest.mark.parametrize(
+    'output_schema_with_tools_allowed',
+    [
+        False,
+        True,
+    ],
+)
+async def test_output_schema_request_processor(
+    output_schema_with_tools_allowed, mocker
+):
   """Test that output schema processor adds set_model_response tool."""
   from google.adk.flows.llm_flows._output_schema_processor import _OutputSchemaRequestProcessor
 
@@ -161,16 +169,29 @@ async def test_output_schema_request_processor():
   llm_request = LlmRequest()
   processor = _OutputSchemaRequestProcessor()
 
+  can_use_output_schema_with_tools = mocker.patch(
+      'google.adk.flows.llm_flows._output_schema_processor.can_use_output_schema_with_tools',
+      mock.MagicMock(return_value=output_schema_with_tools_allowed),
+  )
+
   # Process the request
   events = []
   async for event in processor.run_async(invocation_context, llm_request):
     events.append(event)
 
-  # Should have added set_model_response tool
-  assert 'set_model_response' in llm_request.tools_dict
+  if not output_schema_with_tools_allowed:
+    # Should have added set_model_response tool if output schema with tools is
+    # allowed
+    assert 'set_model_response' in llm_request.tools_dict
+    # Should have added instruction about using set_model_response
+    assert 'set_model_response' in llm_request.config.system_instruction
+  else:
+    # Should skip modifying LlmRequest
+    assert not llm_request.tools_dict
+    assert not llm_request.config.system_instruction
 
-  # Should have added instruction about using set_model_response
-  assert 'set_model_response' in llm_request.config.system_instruction
+  # Should have checked if output schema can be used with tools
+  can_use_output_schema_with_tools.assert_called_once_with(agent.model)
 
 
 @pytest.mark.asyncio

tests/unittests/utils/test_output_schema_utils.py

@@ -0,0 +1,50 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from google.adk.models.anthropic_llm import Claude
+from google.adk.models.google_llm import Gemini
+from google.adk.utils.output_schema_utils import can_use_output_schema_with_tools
+import pytest
+
+
+@pytest.mark.parametrize(
+    "model, env_value, expected",
+    [
+        ("gemini-2.5-pro", "1", True),
+        ("gemini-2.5-pro", "0", False),
+        ("gemini-2.5-pro", None, False),
+        (Gemini(model="gemini-2.5-pro"), "1", True),
+        (Gemini(model="gemini-2.5-pro"), "0", False),
+        (Gemini(model="gemini-2.5-pro"), None, False),
+        ("gemini-2.0-flash", "1", True),
+        ("gemini-2.0-flash", "0", False),
+        ("gemini-2.0-flash", None, False),
+        ("gemini-1.5-pro", "1", False),
+        ("gemini-1.5-pro", "0", False),
+        ("gemini-1.5-pro", None, False),
+        (Claude(model="claude-3.7-sonnet"), "1", False),
+        (Claude(model="claude-3.7-sonnet"), "0", False),
+        (Claude(model="claude-3.7-sonnet"), None, False),
+    ],
+)
+def test_can_use_output_schema_with_tools(
+    monkeypatch, model, env_value, expected
+):
+  """Test can_use_output_schema_with_tools."""
+  if env_value is not None:
+    monkeypatch.setenv("GOOGLE_GENAI_USE_VERTEXAI", env_value)
+  else:
+    monkeypatch.delenv("GOOGLE_GENAI_USE_VERTEXAI", raising=False)
+  assert can_use_output_schema_with_tools(model) == expected