Support chaining for model callbacks

(before/after) model callbacks are invoked throughout the provided chain until one callback does not return None. Callbacks can be async and sync.

PiperOrigin-RevId: 755565583

src/google/adk/agents/llm_agent.py

@@ -47,15 +47,26 @@ from .readonly_context import ReadonlyContext
 
 logger = logging.getLogger(__name__)
 
-
+_SingleBeforeModelCallback: TypeAlias = Callable[
-BeforeModelCallback: TypeAlias = Callable[
     [CallbackContext, LlmRequest],
     Union[Awaitable[Optional[LlmResponse]], Optional[LlmResponse]],
 ]
-AfterModelCallback: TypeAlias = Callable[
+
+BeforeModelCallback: TypeAlias = Union[
+    _SingleBeforeModelCallback,
+    list[_SingleBeforeModelCallback],
+]
+
+_SingleAfterModelCallback: TypeAlias = Callable[
     [CallbackContext, LlmResponse],
     Union[Awaitable[Optional[LlmResponse]], Optional[LlmResponse]],
 ]
+
+AfterModelCallback: TypeAlias = Union[
+    _SingleAfterModelCallback,
+    list[_SingleAfterModelCallback],
+]
+
 BeforeToolCallback: TypeAlias = Callable[
     [BaseTool, dict[str, Any], ToolContext],
     Union[Awaitable[Optional[dict]], Optional[dict]],
@@ -174,7 +185,11 @@ class LlmAgent(BaseAgent):
 
   # Callbacks - Start
   before_model_callback: Optional[BeforeModelCallback] = None
-  """Called before calling the LLM.
+  """Callback or list of callbacks to be called before calling the LLM.
+
+  When a list of callbacks is provided, the callbacks will be called in the
+  order they are listed until a callback does not return None.
+
   Args:
     callback_context: CallbackContext,
     llm_request: LlmRequest, The raw model request. Callback can mutate the
@@ -185,7 +200,10 @@ class LlmAgent(BaseAgent):
     skipped and the provided content will be returned to user.
   """
   after_model_callback: Optional[AfterModelCallback] = None
-  """Called after calling LLM.
+  """Callback or list of callbacks to be called after calling the LLM.
+
+  When a list of callbacks is provided, the callbacks will be called in the
+  order they are listed until a callback does not return None.
 
   Args:
     callback_context: CallbackContext,
@@ -285,6 +303,32 @@ class LlmAgent(BaseAgent):
     """
     return [_convert_tool_union_to_tool(tool) for tool in self.tools]
 
+  @property
+  def canonical_before_model_callbacks(
+      self,
+  ) -> list[_SingleBeforeModelCallback]:
+    """The resolved self.before_model_callback field as a list of _SingleBeforeModelCallback.
+
+    This method is only for use by Agent Development Kit.
+    """
+    if not self.before_model_callback:
+      return []
+    if isinstance(self.before_model_callback, list):
+      return self.before_model_callback
+    return [self.before_model_callback]
+
+  @property
+  def canonical_after_model_callbacks(self) -> list[_SingleAfterModelCallback]:
+    """The resolved self.after_model_callback field as a list of _SingleAfterModelCallback.
+
+    This method is only for use by Agent Development Kit.
+    """
+    if not self.after_model_callback:
+      return []
+    if isinstance(self.after_model_callback, list):
+      return self.after_model_callback
+    return [self.after_model_callback]
+
   @property
   def _llm_flow(self) -> BaseLlmFlow:
     if (

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

@@ -193,8 +193,9 @@ class BaseLlmFlow(ABC):
     """Receive data from model and process events using BaseLlmConnection."""
     def get_author(llm_response):
       """Get the author of the event.
-      
+
-      When the model returns transcription, the author is "user". Otherwise, the author is the agent.
+      When the model returns transcription, the author is "user". Otherwise, the
+      author is the agent.
       """
       if llm_response and llm_response.content and llm_response.content.role == "user":
         return "user"
@@ -509,20 +510,21 @@ class BaseLlmFlow(ABC):
     if not isinstance(agent, LlmAgent):
       return
 
-    if not agent.before_model_callback:
+    if not agent.canonical_before_model_callbacks:
       return
 
     callback_context = CallbackContext(
         invocation_context, event_actions=model_response_event.actions
     )
-    before_model_callback_content = agent.before_model_callback(
-        callback_context=callback_context, llm_request=llm_request
-    )
 
-    if inspect.isawaitable(before_model_callback_content):
+    for callback in agent.canonical_before_model_callbacks:
-      before_model_callback_content = await before_model_callback_content
+      before_model_callback_content = callback(
-
+          callback_context=callback_context, llm_request=llm_request
-    return before_model_callback_content
+      )
+      if inspect.isawaitable(before_model_callback_content):
+        before_model_callback_content = await before_model_callback_content
+      if before_model_callback_content:
+        return before_model_callback_content
 
   async def _handle_after_model_callback(
       self,
@@ -536,20 +538,21 @@ class BaseLlmFlow(ABC):
     if not isinstance(agent, LlmAgent):
       return
 
-    if not agent.after_model_callback:
+    if not agent.canonical_after_model_callbacks:
       return
 
     callback_context = CallbackContext(
         invocation_context, event_actions=model_response_event.actions
     )
-    after_model_callback_content = agent.after_model_callback(
-        callback_context=callback_context, llm_response=llm_response
-    )
 
-    if inspect.isawaitable(after_model_callback_content):
+    for callback in agent.canonical_after_model_callbacks:
-      after_model_callback_content = await after_model_callback_content
+      after_model_callback_content = callback(
-
+          callback_context=callback_context, llm_response=llm_response
-    return after_model_callback_content
+      )
+      if inspect.isawaitable(after_model_callback_content):
+        after_model_callback_content = await after_model_callback_content
+      if after_model_callback_content:
+        return after_model_callback_content
 
   def _finalize_model_response_event(
       self,

tests/unittests/agents/test_agent_callbacks.py

@@ -0,0 +1,209 @@
+# 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 typing import Any
+from typing import Optional
+
+from google.adk.agents.callback_context import CallbackContext
+from google.adk.agents.llm_agent import Agent
+from google.adk.models import LlmRequest
+from google.adk.models import LlmResponse
+from google.genai import types
+from google.genai import types
+from pydantic import BaseModel
+import pytest
+
+from .. import utils
+
+
+class MockAgentCallback(BaseModel):
+  mock_response: str
+
+  def __call__(
+      self,
+      callback_context: CallbackContext,
+  ) -> types.Content:
+    return types.Content(parts=[types.Part(text=self.mock_response)])
+
+
+class MockAsyncAgentCallback(BaseModel):
+  mock_response: str
+
+  async def __call__(
+      self,
+      callback_context: CallbackContext,
+  ) -> types.Content:
+    return types.Content(parts=[types.Part(text=self.mock_response)])
+
+
+def noop_callback(**kwargs) -> Optional[LlmResponse]:
+  pass
+
+
+async def async_noop_callback(**kwargs) -> Optional[LlmResponse]:
+  pass
+
+
+@pytest.mark.asyncio
+async def test_before_agent_callback():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_agent_callback=MockAgentCallback(
+          mock_response='before_agent_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'before_agent_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_after_agent_callback():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      after_agent_callback=MockAgentCallback(
+          mock_response='after_agent_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'agent_response'),
+      ('root_agent', 'after_agent_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_before_agent_callback_noop():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_agent_callback=noop_callback,
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'agent_response'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_after_agent_callback_noop():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_agent_callback=noop_callback,
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'agent_response'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_before_agent_callback():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_agent_callback=MockAsyncAgentCallback(
+          mock_response='async_before_agent_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'async_before_agent_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_after_agent_callback():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      after_agent_callback=MockAsyncAgentCallback(
+          mock_response='async_after_agent_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'agent_response'),
+      ('root_agent', 'async_after_agent_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_before_agent_callback_noop():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_agent_callback=async_noop_callback,
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'agent_response'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_after_agent_callback_noop():
+  responses = ['agent_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_agent_callback=async_noop_callback,
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'agent_response'),
+  ]

tests/unittests/agents/test_model_callback_chain.py

@@ -0,0 +1,242 @@
+# 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 enum import Enum
+from functools import partial
+from typing import Any
+from typing import List
+from typing import Optional
+from unittest import mock
+
+from google.adk.agents.callback_context import CallbackContext
+from google.adk.agents.llm_agent import Agent
+from google.adk.models import LlmRequest
+from google.adk.models import LlmResponse
+from google.genai import types
+from pydantic import BaseModel
+import pytest
+
+from .. import utils
+
+
+class CallbackType(Enum):
+  SYNC = 1
+  ASYNC = 2
+
+
+async def mock_async_before_cb_side_effect(
+    callback_context: CallbackContext,
+    llm_request: LlmRequest,
+    ret_value=None,
+):
+  if ret_value:
+    return LlmResponse(
+        content=utils.ModelContent([types.Part.from_text(text=ret_value)])
+    )
+  return None
+
+
+def mock_sync_before_cb_side_effect(
+    callback_context: CallbackContext,
+    llm_request: LlmRequest,
+    ret_value=None,
+):
+  if ret_value:
+    return LlmResponse(
+        content=utils.ModelContent([types.Part.from_text(text=ret_value)])
+    )
+  return None
+
+
+async def mock_async_after_cb_side_effect(
+    callback_context: CallbackContext,
+    llm_response: LlmResponse,
+    ret_value=None,
+):
+  if ret_value:
+    return LlmResponse(
+        content=utils.ModelContent([types.Part.from_text(text=ret_value)])
+    )
+  return None
+
+
+def mock_sync_after_cb_side_effect(
+    callback_context: CallbackContext,
+    llm_response: LlmResponse,
+    ret_value=None,
+):
+  if ret_value:
+    return LlmResponse(
+        content=utils.ModelContent([types.Part.from_text(text=ret_value)])
+    )
+  return None
+
+
+CALLBACK_PARAMS = [
+    pytest.param(
+        [
+            (None, CallbackType.SYNC),
+            ("callback_2_response", CallbackType.ASYNC),
+            ("callback_3_response", CallbackType.SYNC),
+            (None, CallbackType.ASYNC),
+        ],
+        "callback_2_response",
+        [1, 1, 0, 0],
+        id="middle_async_callback_returns",
+    ),
+    pytest.param(
+        [
+            (None, CallbackType.SYNC),
+            (None, CallbackType.ASYNC),
+            (None, CallbackType.SYNC),
+            (None, CallbackType.ASYNC),
+        ],
+        "model_response",
+        [1, 1, 1, 1],
+        id="all_callbacks_return_none",
+    ),
+    pytest.param(
+        [
+            ("callback_1_response", CallbackType.SYNC),
+            ("callback_2_response", CallbackType.ASYNC),
+        ],
+        "callback_1_response",
+        [1, 0],
+        id="first_sync_callback_returns",
+    ),
+]
+
+
+@pytest.mark.parametrize(
+    "callbacks, expected_response, expected_calls",
+    CALLBACK_PARAMS,
+)
+@pytest.mark.asyncio
+async def test_before_model_callbacks_chain(
+    callbacks: List[tuple[str, int]],
+    expected_response: str,
+    expected_calls: List[int],
+):
+  responses = ["model_response"]
+  mock_model = utils.MockModel.create(responses=responses)
+
+  mock_cbs = []
+  for response, callback_type in callbacks:
+
+    if callback_type == CallbackType.ASYNC:
+      mock_cb = mock.AsyncMock(
+          side_effect=partial(
+              mock_async_before_cb_side_effect, ret_value=response
+          )
+      )
+    else:
+      mock_cb = mock.Mock(
+          side_effect=partial(
+              mock_sync_before_cb_side_effect, ret_value=response
+          )
+      )
+    mock_cbs.append(mock_cb)
+  # Create agent with multiple callbacks
+  agent = Agent(
+      name="root_agent",
+      model=mock_model,
+      before_model_callback=[mock_cb for mock_cb in mock_cbs],
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  result = await runner.run_async_with_new_session("test")
+  assert utils.simplify_events(result) == [
+      ("root_agent", expected_response),
+  ]
+
+  # Assert that the callbacks were called the expected number of times
+  for i, mock_cb in enumerate(mock_cbs):
+    expected_calls_count = expected_calls[i]
+    if expected_calls_count == 1:
+      if isinstance(mock_cb, mock.AsyncMock):
+        mock_cb.assert_awaited_once()
+      else:
+        mock_cb.assert_called_once()
+    elif expected_calls_count == 0:
+      if isinstance(mock_cb, mock.AsyncMock):
+        mock_cb.assert_not_awaited()
+      else:
+        mock_cb.assert_not_called()
+    else:
+      if isinstance(mock_cb, mock.AsyncMock):
+        mock_cb.assert_awaited(expected_calls_count)
+      else:
+        mock_cb.assert_called(expected_calls_count)
+
+
+@pytest.mark.parametrize(
+    "callbacks, expected_response, expected_calls",
+    CALLBACK_PARAMS,
+)
+@pytest.mark.asyncio
+async def test_after_model_callbacks_chain(
+    callbacks: List[tuple[str, int]],
+    expected_response: str,
+    expected_calls: List[int],
+):
+  responses = ["model_response"]
+  mock_model = utils.MockModel.create(responses=responses)
+
+  mock_cbs = []
+  for response, callback_type in callbacks:
+
+    if callback_type == CallbackType.ASYNC:
+      mock_cb = mock.AsyncMock(
+          side_effect=partial(
+              mock_async_after_cb_side_effect, ret_value=response
+          )
+      )
+    else:
+      mock_cb = mock.Mock(
+          side_effect=partial(
+              mock_sync_after_cb_side_effect, ret_value=response
+          )
+      )
+    mock_cbs.append(mock_cb)
+  # Create agent with multiple callbacks
+  agent = Agent(
+      name="root_agent",
+      model=mock_model,
+      after_model_callback=[mock_cb for mock_cb in mock_cbs],
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  result = await runner.run_async_with_new_session("test")
+  assert utils.simplify_events(result) == [
+      ("root_agent", expected_response),
+  ]
+
+  # Assert that the callbacks were called the expected number of times
+  for i, mock_cb in enumerate(mock_cbs):
+    expected_calls_count = expected_calls[i]
+    if expected_calls_count == 1:
+      if isinstance(mock_cb, mock.AsyncMock):
+        mock_cb.assert_awaited_once()
+      else:
+        mock_cb.assert_called_once()
+    elif expected_calls_count == 0:
+      if isinstance(mock_cb, mock.AsyncMock):
+        mock_cb.assert_not_awaited()
+      else:
+        mock_cb.assert_not_called()
+    else:
+      if isinstance(mock_cb, mock.AsyncMock):
+        mock_cb.assert_awaited(expected_calls_count)
+      else:
+        mock_cb.assert_called(expected_calls_count)

tests/unittests/agents/test_model_callbacks.py

@@ -0,0 +1,210 @@
+# 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 typing import Any
+from typing import Optional
+
+from google.adk.agents.callback_context import CallbackContext
+from google.adk.agents.llm_agent import Agent
+from google.adk.models import LlmRequest
+from google.adk.models import LlmResponse
+from google.genai import types
+from pydantic import BaseModel
+import pytest
+
+from .. import utils
+
+
+class MockBeforeModelCallback(BaseModel):
+  mock_response: str
+
+  def __call__(
+      self,
+      callback_context: CallbackContext,
+      llm_request: LlmRequest,
+  ) -> LlmResponse:
+    return LlmResponse(
+        content=utils.ModelContent(
+            [types.Part.from_text(text=self.mock_response)]
+        )
+    )
+
+
+class MockAfterModelCallback(BaseModel):
+  mock_response: str
+
+  def __call__(
+      self,
+      callback_context: CallbackContext,
+      llm_response: LlmResponse,
+  ) -> LlmResponse:
+    return LlmResponse(
+        content=utils.ModelContent(
+            [types.Part.from_text(text=self.mock_response)]
+        )
+    )
+
+
+class MockAsyncBeforeModelCallback(BaseModel):
+  mock_response: str
+
+  async def __call__(
+      self,
+      callback_context: CallbackContext,
+      llm_request: LlmRequest,
+  ) -> LlmResponse:
+    return LlmResponse(
+        content=utils.ModelContent(
+            [types.Part.from_text(text=self.mock_response)]
+        )
+    )
+
+
+class MockAsyncAfterModelCallback(BaseModel):
+  mock_response: str
+
+  async def __call__(
+      self,
+      callback_context: CallbackContext,
+      llm_response: LlmResponse,
+  ) -> LlmResponse:
+    return LlmResponse(
+        content=utils.ModelContent(
+            [types.Part.from_text(text=self.mock_response)]
+        )
+    )
+
+
+def noop_callback(**kwargs) -> Optional[LlmResponse]:
+  pass
+
+
+async def async_noop_callback(**kwargs) -> Optional[LlmResponse]:
+  pass
+
+
+@pytest.mark.asyncio
+async def test_before_model_callback():
+  responses = ['model_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_model_callback=MockBeforeModelCallback(
+          mock_response='before_model_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'before_model_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_before_model_callback_noop():
+  responses = ['model_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_model_callback=noop_callback,
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'model_response'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_after_model_callback():
+  responses = ['model_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      after_model_callback=MockAfterModelCallback(
+          mock_response='after_model_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'after_model_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_before_model_callback():
+  responses = ['model_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_model_callback=MockAsyncBeforeModelCallback(
+          mock_response='async_before_model_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'async_before_model_callback'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_before_model_callback_noop():
+  responses = ['model_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      before_model_callback=async_noop_callback,
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'model_response'),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_async_after_model_callback():
+  responses = ['model_response']
+  mock_model = utils.MockModel.create(responses=responses)
+  agent = Agent(
+      name='root_agent',
+      model=mock_model,
+      after_model_callback=MockAsyncAfterModelCallback(
+          mock_response='async_after_model_callback'
+      ),
+  )
+
+  runner = utils.TestInMemoryRunner(agent)
+  assert utils.simplify_events(
+      await runner.run_async_with_new_session('test')
+  ) == [
+      ('root_agent', 'async_after_model_callback'),
+  ]