diff --git a/shiny/ui/_chat.py b/shiny/ui/_chat.py
index 99a399109..98f1defad 100644
--- a/shiny/ui/_chat.py
+++ b/shiny/ui/_chat.py
@@ -507,7 +507,12 @@ async def append_message(self, message: Any) -> None:
         await self._append_message(message)
 
     async def _append_message(
-        self, message: Any, *, chunk: ChunkOption = False, stream_id: str | None = None
+        self,
+        message: Any,
+        *,
+        chunk: ChunkOption = False,
+        stream_id: str | None = None,
+        normalizer: Callable[[object], str] | None = None,
     ) -> None:
         # If currently we're in a stream, handle other messages (outside the stream) later
         if not self._can_append_message(stream_id):
@@ -519,6 +524,15 @@ async def _append_message(
         if chunk == "end":
             self._current_stream_id = None
 
+        # Apply the user provided normalizer, if any
+        if normalizer is not None:
+            res = normalizer(message)
+            if not isinstance(res, str):
+                raise ValueError(
+                    f"Normalizer function must return a string, got {type(res)}"
+                )
+            message = {"content": res, "role": "assistant"}
+
         if chunk is False:
             msg = normalize_message(message)
             chunk_content = None
@@ -539,7 +553,11 @@ async def _append_message(
         msg = self._store_message(msg, chunk=chunk)
         await self._send_append_message(msg, chunk=chunk)
 
-    async def append_message_stream(self, message: Iterable[Any] | AsyncIterable[Any]):
+    async def append_message_stream(
+        self,
+        message: Iterable[Any] | AsyncIterable[Any],
+        normalizer: Callable[[object], str] | None = None,
+    ) -> None:
         """
         Append a message as a stream of message chunks.
 
@@ -550,6 +568,11 @@ async def append_message_stream(self, message: Iterable[Any] | AsyncIterable[Any
             message chunk formats are supported, including a string, a dictionary with
             `content` and `role` keys, or a relevant chat completion object from
             platforms like OpenAI, Anthropic, Ollama, and others.
+        normalizer
+            A function to apply to each message chunk (i.e., each item of the `message`
+            iterator) before appending it to the chat. This is useful for handling
+            response formats that `Chat` may not already natively support. The function
+            should take a message chunk and return a string.
 
         Note
         ----
@@ -562,7 +585,7 @@ async def append_message_stream(self, message: Iterable[Any] | AsyncIterable[Any
         # Run the stream in the background to get non-blocking behavior
         @reactive.extended_task
         async def _stream_task():
-            await self._append_message_stream(message)
+            await self._append_message_stream(message, normalizer)
 
         _stream_task()
 
@@ -582,7 +605,11 @@ async def _handle_error():
         ctx.on_invalidate(_handle_error.destroy)
         self._effects.append(_handle_error)
 
-    async def _append_message_stream(self, message: AsyncIterable[Any]):
+    async def _append_message_stream(
+        self,
+        message: AsyncIterable[Any],
+        normalizer: Callable[[object], str] | None = None,
+    ) -> None:
         id = _utils.private_random_id()
 
         empty = ChatMessage(content="", role="assistant")
@@ -590,7 +617,9 @@ async def _append_message_stream(self, message: AsyncIterable[Any]):
 
         try:
             async for msg in message:
-                await self._append_message(msg, chunk=True, stream_id=id)
+                await self._append_message(
+                    msg, chunk=True, stream_id=id, normalizer=normalizer
+                )
         finally:
             await self._append_message(empty, chunk="end", stream_id=id)
             await self._flush_pending_messages()