feat: enable server side MCP and disable all other AFC when server side MCP is configured.

google/genai/_extra_utils.py

@@ -141,9 +141,12 @@ def find_afc_incompatible_tool_indexes(
     return incompatible_tools_indexes
 
   for index, tool in enumerate(config_model.tools):
-    if isinstance(tool, types.Tool) and tool.function_declarations:
+    if not isinstance(tool, types.Tool):
+      continue
+    if tool.function_declarations:
+      incompatible_tools_indexes.append(index)
+    if tool.mcp_servers:
       incompatible_tools_indexes.append(index)
-
   return incompatible_tools_indexes
 
 

google/genai/_live_converters.py

@@ -1397,6 +1397,13 @@ def _Tool_to_mldev(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    setv(
+        to_object,
+        ['mcpServers'],
+        [item for item in getv(from_object, ['mcp_servers'])],
+    )
+
   return to_object
 
 
@@ -1450,6 +1457,9 @@ def _Tool_to_vertex(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    raise ValueError('mcp_servers parameter is not supported in Vertex AI.')
+
   return to_object
 
 

google/genai/_tokens_converters.py

@@ -522,4 +522,11 @@ def _Tool_to_mldev(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    setv(
+        to_object,
+        ['mcpServers'],
+        [item for item in getv(from_object, ['mcp_servers'])],
+    )
+
   return to_object

google/genai/batches.py

@@ -1498,6 +1498,13 @@ def _Tool_to_mldev(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    setv(
+        to_object,
+        ['mcpServers'],
+        [item for item in getv(from_object, ['mcp_servers'])],
+    )
+
   return to_object
 
 

google/genai/caches.py

@@ -704,6 +704,13 @@ def _Tool_to_mldev(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    setv(
+        to_object,
+        ['mcpServers'],
+        [item for item in getv(from_object, ['mcp_servers'])],
+    )
+
   return to_object
 
 
@@ -757,6 +764,9 @@ def _Tool_to_vertex(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    raise ValueError('mcp_servers parameter is not supported in Vertex AI.')
+
   return to_object
 
 

google/genai/models.py

@@ -3770,6 +3770,13 @@ def _Tool_to_mldev(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    setv(
+        to_object,
+        ['mcpServers'],
+        [item for item in getv(from_object, ['mcp_servers'])],
+    )
+
   return to_object
 
 
@@ -3824,6 +3831,9 @@ def _Tool_to_vertex(
   if getv(from_object, ['url_context']) is not None:
     setv(to_object, ['urlContext'], getv(from_object, ['url_context']))
 
+  if getv(from_object, ['mcp_servers']) is not None:
+    raise ValueError('mcp_servers parameter is not supported in Vertex AI.')
+
   return to_object
 
 
@@ -5600,7 +5610,7 @@ def generate_content(
             'Tools at indices [%s] are not compatible with automatic function '
             'calling (AFC). AFC is disabled. If AFC is intended, please '
             'include python callables in the tool list, and do not include '
-            'function declaration in the tool list.',
+            'function declaration and MCP server in the tool list.',
             indices_str,
         )
       return self._generate_content(
@@ -7469,7 +7479,7 @@ async def generate_content(
             'Tools at indices [%s] are not compatible with automatic function '
             'calling (AFC). AFC is disabled. If AFC is intended, please '
             'include python callables in the tool list, and do not include '
-            'function declaration in the tool list.',
+            'function declaration and MCP server in the tool list.',
             indices_str,
         )
       return await self._generate_content(
@@ -7633,7 +7643,7 @@ async def base_async_generator(model, contents, config):  # type: ignore[no-unty
             'Tools at indices [%s] are not compatible with automatic function '
             'calling (AFC). AFC is disabled. If AFC is intended, please '
             'include python callables in the tool list, and do not include '
-            'function declaration in the tool list.',
+            'function declaration and MCP server in the tool list.',
             indices_str,
         )
       response = await self._generate_content_stream(

google/genai/tests/afc/test_find_afc_incompatible_tool_indexes.py

@@ -83,6 +83,7 @@ def test_empty_tools_list_returns_empty_list():
 
 def test_all_compatible_tools_returns_empty_list_with_empty_fd():
     """Verifies that an empty list is returned when all tools are compatible.
+
     A tool is compatible if it's not a `types.Tool` or if its
     `function_declarations` attribute is empty or None from config.
     """
@@ -118,6 +119,7 @@ def test_all_compatible_tools_returns_empty_list_with_empty_fd():
 
 def test_all_compatible_tools_returns_empty_list_with_none_fd():
     """Verifies that an empty list is returned when all tools are compatible.
+
     A tool is compatible if it's not a `types.Tool` or if its
     `function_declarations` attribute is empty or None from config.
     """
@@ -153,6 +155,7 @@ def test_all_compatible_tools_returns_empty_list_with_none_fd():
 
 def test_all_compatible_tools_returns_empty_list():
     """Verifies that an empty list is returned when all tools are compatible.
+
     A tool is compatible if it's not a `types.Tool` or if its
     `function_declarations` attribute is empty or None from config.
     """
@@ -211,8 +214,7 @@ def test_single_incompatible_tool():
 
 
 def test_multiple_incompatible_tools():
-    """Verifies that all correct indexes are returned for multiple incompatible
-    tools. """
+    """Verifies correct indexes are returned for multiple incompatible tools."""
     result = find_afc_incompatible_tool_indexes(
         config=types.GenerateContentConfig(
             tools=[
@@ -238,3 +240,29 @@ def test_multiple_incompatible_tools():
         )
     )
     assert result == [2, 5]
+
+def test_mcp_tool_incompatible():
+    """Verifies correct indexes are returned for multiple incompatible tools."""
+    result = find_afc_incompatible_tool_indexes(
+        config=types.GenerateContentConfig(
+            tools=[
+                types.Tool(
+                    google_search_retrieval=types.GoogleSearchRetrieval()
+                ),
+                types.Tool(retrieval=types.Retrieval()),
+                types.Tool(
+                    function_declarations=[
+                        types.FunctionDeclaration(name='test_function')
+                    ]
+                ),
+                types.Tool(code_execution=types.ToolCodeExecution()),
+
+                get_weather_tool,
+                mcp_to_genai_tool_adapter,
+                types.Tool(
+                    mcp_servers=[types.McpServer(name='test_mcp_server')]
+                ),
+            ]
+        )
+    )
+    assert result == [2, 6]

google/genai/tests/chats/test_send_message.py

@@ -768,9 +768,8 @@ def test_mcp_tools(client):
               )
           ],},
   )
-  response = chat.send_message('What is the weather in Boston?');
-  response = chat.send_message('What is the weather in San Francisco?');
-
+  response = chat.send_message('What is the weather in Boston?')
+  response = chat.send_message('What is the weather in San Francisco?')
 
 
 def test_mcp_tools_stream(client):
@@ -842,3 +841,101 @@ async def test_async_mcp_tools_stream(client):
     'What is the weather in San Francisco?'
   ):
     pass
+
+
+def test_server_side_mcp_tools(client):
+   with pytest_helper.exception_if_vertex(client, ValueError):
+    chat = client.chats.create(
+        model='gemini-2.5-flash',
+        config={
+            'tools': [
+                {
+                    'mcp_servers': [
+                        {
+                            'name': 'weather_server',
+                            'streamable_http_transport': {
+                                'url': (
+                                    'https://gemini-api-demos.uc.r.appspot.com/mcp'
+                                ),
+                                'headers': {
+                                    'AUTHORIZATION': 'Bearer github_pat_XXXX',
+                                },
+                                'timeout': '10s',
+                            },
+                        },
+                    ],
+                },
+            ],
+        },
+    )
+    response = chat.send_message('What is the weather in Boston on 02/02/2026?')
+    response = chat.send_message(
+        'What is the weather in San Francisco on 02/02/2026?'
+    )
+
+
+def test_server_side_mcp_tools_stream(client):
+  with pytest_helper.exception_if_vertex(client, ValueError):
+    chat = client.chats.create(
+        model='gemini-2.5-flash',
+        config={
+            'tools': [
+                {
+                    'mcp_servers': [
+                        {
+                            'name': 'weather_server',
+                            'streamable_http_transport': {
+                                'url': (
+                                    'https://gemini-api-demos.uc.r.appspot.com/mcp'
+                                ),
+                                'headers': {
+                                    'AUTHORIZATION': 'Bearer github_pat_XXXX',
+                                },
+                                'timeout': '10s',
+                            },
+                        },
+                    ],
+                },
+            ],
+        },
+    )
+    for chunk in chat.send_message_stream(
+        'What is the weather in Boston on 02/02/2026?'
+    ):
+      pass
+    for chunk in chat.send_message_stream(
+        'What is the weather in San Francisco on 02/02/2026?'
+    ):
+      pass
+
+
+@pytest.mark.asyncio
+async def test_async_server_side_mcp_tools(client):
+  with pytest_helper.exception_if_vertex(client, ValueError):
+    chat = client.aio.chats.create(
+        model='gemini-2.5-flash',
+        config={
+            'tools': [
+                {
+                    'mcp_servers': [
+                        {
+                            'name': 'weather_server',
+                            'streamable_http_transport': {
+                                'url': (
+                                    'https://gemini-api-demos.uc.r.appspot.com/mcp'
+                                ),
+                                'headers': {
+                                    'AUTHORIZATION': 'Bearer github_pat_XXXX',
+                                },
+                                'timeout': '10s',
+                            },
+                        },
+                    ],
+                },
+            ],
+        },
+    )
+    await chat.send_message('What is the weather in Boston on 02/02/2026?')
+    await chat.send_message(
+        'What is the weather in San Francisco on 02/02/2026?'
+    )

google/genai/tests/models/test_generate_content_tools.py

@@ -1759,3 +1759,68 @@ async def test_function_declaration_with_callable_async_stream(client):
         },
     ):
       pass
+
+def test_server_side_mcp_only(client):
+  """Test server side mcp, happy path."""
+  with pytest_helper.exception_if_vertex(client, ValueError):
+    response = client.models.generate_content(
+        model='gemini-2.5-pro',
+        contents=('What is the weather like in New York (NY) on 02/02/2026?'),
+        config=types.GenerateContentConfig(
+            tools=[types.Tool(
+                mcp_servers=[types.McpServer(
+                    name='get_weather',
+                    streamable_http_transport=types.StreamableHttpTransport(
+                        url='https://gemini-api-demos.uc.r.appspot.com/mcp',
+                        headers={'AUTHORIZATION': 'Bearer github_pat_XXXX'},
+                    ),
+                )]
+            )]
+        )
+    )
+    assert response.text
+
+@pytest.mark.asyncio
+async def test_server_side_mcp_only_async(client):
+  """Test server side mcp, happy path."""
+  with pytest_helper.exception_if_vertex(client, ValueError):
+    response = await client.aio.models.generate_content(
+        model='gemini-2.5-flash',
+        contents=(
+            'What is the weather like in New York on 02/02/2026?'
+        ),
+        config=types.GenerateContentConfig(
+            tools=[types.Tool(
+                mcp_servers=[types.McpServer(
+                    name='get_weather',
+                    streamable_http_transport=types.StreamableHttpTransport(
+                        url='https://gemini-api-demos.uc.r.appspot.com/mcp',
+                        headers={'AUTHORIZATION': 'Bearer github_pat_XXXX'},
+                    ),
+                )]
+
+            )]
+        )
+    )
+    assert response.text
+
+def test_server_side_mcp_only_stream(client):
+  """Test server side mcp, happy path."""
+  with pytest_helper.exception_if_vertex(client, ValueError):
+    response = client.models.generate_content_stream(
+        model='gemini-2.5-pro',
+        contents=('What is the weather like in New York (NY) on 02/02/2026?'),
+        config=types.GenerateContentConfig(
+            tools=[types.Tool(
+                mcp_servers=[types.McpServer(
+                    name='get_weather',
+                    streamable_http_transport=types.StreamableHttpTransport(
+                        url='https://gemini-api-demos.uc.r.appspot.com/mcp',
+                        headers={'AUTHORIZATION': 'Bearer github_pat_XXXX'},
+                    ),
+                )]
+            )]
+        )
+    )
+    for chunk in response:
+      pass