diff --git a/python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py b/python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py
index 3765c2ad2afd..8fcec588fc68 100644
--- a/python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py
+++ b/python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py
@@ -766,6 +766,7 @@ async def create_stream(
         stop_reason: Optional[str] = None
 
         first_chunk = True
+        serialized_messages: List[Dict[str, Any]] = [self._serialize_message(msg) for msg in anthropic_messages]
 
         # Process the stream
         async for chunk in stream:
@@ -774,7 +775,7 @@ async def create_stream(
                 # Emit the start event.
                 logger.info(
                     LLMStreamStartEvent(
-                        messages=cast(List[Dict[str, Any]], anthropic_messages),
+                        messages=serialized_messages,
                     )
                 )
             # Handle different event types