diff --git a/python/packages/autogen-core/src/autogen_core/tools/_function_tool.py b/python/packages/autogen-core/src/autogen_core/tools/_function_tool.py
index b43e061350e..12cee716f23 100644
--- a/python/packages/autogen-core/src/autogen_core/tools/_function_tool.py
+++ b/python/packages/autogen-core/src/autogen_core/tools/_function_tool.py
@@ -1,8 +1,8 @@
 import asyncio
 import functools
+import warnings
 from textwrap import dedent
 from typing import Any, Callable, Sequence
-import warnings
 
 from pydantic import BaseModel
 from typing_extensions import Self
diff --git a/python/packages/autogen-ext/src/autogen_ext/models/cache/_chat_completion_cache.py b/python/packages/autogen-ext/src/autogen_ext/models/cache/_chat_completion_cache.py
index 79ed5f1660a..15ea1cfd240 100644
--- a/python/packages/autogen-ext/src/autogen_ext/models/cache/_chat_completion_cache.py
+++ b/python/packages/autogen-ext/src/autogen_ext/models/cache/_chat_completion_cache.py
@@ -3,7 +3,7 @@
 import warnings
 from typing import Any, AsyncGenerator, List, Mapping, Optional, Sequence, Union, cast
 
-from autogen_core import CacheStore, CancellationToken
+from autogen_core import CacheStore, CancellationToken, InMemoryStore
 from autogen_core.models import (
     ChatCompletionClient,
     CreateResult,
@@ -74,11 +74,16 @@ async def main():
         client (ChatCompletionClient): The original ChatCompletionClient to wrap.
         store (CacheStore): A store object that implements get and set methods.
             The user is responsible for managing the store's lifecycle & clearing it (if needed).
+            Defaults to using in-memory cache.
     """
 
-    def __init__(self, client: ChatCompletionClient, store: CacheStore[CHAT_CACHE_VALUE_TYPE]):
+    def __init__(
+        self,
+        client: ChatCompletionClient,
+        store: Optional[CacheStore[CHAT_CACHE_VALUE_TYPE]] = None,
+    ):
         self.client = client
-        self.store = store
+        self.store = store or InMemoryStore[CHAT_CACHE_VALUE_TYPE]()
 
     def _check_cache(
         self,
diff --git a/python/packages/autogen-ext/tests/models/test_chat_completion_cache.py b/python/packages/autogen-ext/tests/models/test_chat_completion_cache.py
index ceb4d9a9f72..5a023b02dff 100644
--- a/python/packages/autogen-ext/tests/models/test_chat_completion_cache.py
+++ b/python/packages/autogen-ext/tests/models/test_chat_completion_cache.py
@@ -2,7 +2,6 @@
 from typing import List, Tuple, Union
 
 import pytest
-from autogen_core import InMemoryStore
 from autogen_core.models import (
     ChatCompletionClient,
     CreateResult,
@@ -10,7 +9,7 @@
     SystemMessage,
     UserMessage,
 )
-from autogen_ext.models.cache import CHAT_CACHE_VALUE_TYPE, ChatCompletionCache
+from autogen_ext.models.cache import ChatCompletionCache
 from autogen_ext.models.replay import ReplayChatCompletionClient
 
 
@@ -21,8 +20,7 @@ def get_test_data() -> Tuple[list[str], list[str], SystemMessage, ChatCompletion
     system_prompt = SystemMessage(content="This is a system prompt")
     replay_client = ReplayChatCompletionClient(responses)
     replay_client.set_cached_bool_value(False)
-    store = InMemoryStore[CHAT_CACHE_VALUE_TYPE]()
-    cached_client = ChatCompletionCache(replay_client, store)
+    cached_client = ChatCompletionCache(replay_client)
 
     return responses, prompts, system_prompt, replay_client, cached_client