[Fix] Serve drops some attributes at serialization

src/transformers/cli/serving/chat_completion.py

@@ -30,33 +30,19 @@
     from fastapi.responses import JSONResponse, StreamingResponse
     from openai.types.chat import (
         ChatCompletion,
+        ChatCompletionMessage,
         ChatCompletionMessageToolCall,
     )
-    from openai.types.chat import (
-        ChatCompletionMessage as OpenAIChatCompletionMessage,
-    )
     from openai.types.chat.chat_completion import Choice
     from openai.types.chat.chat_completion_chunk import (
         ChatCompletionChunk,
+        ChoiceDelta,
         ChoiceDeltaToolCall,
     )
     from openai.types.chat.chat_completion_chunk import Choice as ChoiceChunk
-    from openai.types.chat.chat_completion_chunk import (
-        ChoiceDelta as OpenAIChoiceDelta,
-    )
     from openai.types.chat.completion_create_params import CompletionCreateParamsStreaming
     from openai.types.completion_usage import CompletionUsage
 
-    class ChatCompletionMessage(OpenAIChatCompletionMessage):
-        """OpenAI ``ChatCompletionMessage`` extended with the ``reasoning_content`` field."""
-
-        reasoning_content: str | None = None
-
-    class ChoiceDelta(OpenAIChoiceDelta):
-        """OpenAI ``ChoiceDelta`` extended with the ``reasoning_content`` field."""
-
-        reasoning_content: str | None = None
-
 
 from .utils import (
     BaseGenerateManager,
@@ -413,21 +399,17 @@ def _build_completion(
         Returns:
             `dict`: Serialized ``ChatCompletion`` ready for JSON response.
         """
-        message = ChatCompletionMessage(
-            content=content, role="assistant", tool_calls=tool_calls, reasoning_content=reasoning_content
+        # reasoning_content is added as an extra field (base types set extra="allow")
+        # we use model_validate rather than __init__ to avoid ty raising errors for the extra field
+        message = ChatCompletionMessage.model_validate(
+            {"content": content, "role": "assistant", "tool_calls": tool_calls, "reasoning_content": reasoning_content}
         )
         result = ChatCompletion(
             id=request_id,
             created=int(time.time()),
             object="chat.completion",
             model=model_id,
-            choices=[
-                Choice(
-                    index=0,
-                    message=message,
-                    finish_reason=finish_reason,
-                )
-            ],
+            choices=[Choice(index=0, message=message, finish_reason=finish_reason)],
             usage=usage,
         )
         return result.model_dump(exclude_none=True)
@@ -458,19 +440,16 @@ def _build_chunk_sse(
         Returns:
             `str`: A formatted SSE event string.
         """
+        # reasoning_content is added as an extra field (base types set extra="allow")
+        # we use model_validate rather than __init__ to avoid ty raising errors for the extra field
+        delta = ChoiceDelta.model_validate(
+            {"content": content, "role": role, "tool_calls": tool_calls, "reasoning_content": reasoning_content}
+        )
         chunk = ChatCompletionChunk(
             id=request_id,
             created=int(time.time()),
             model=model,
-            choices=[
-                ChoiceChunk(
-                    delta=ChoiceDelta(
-                        content=content, role=role, tool_calls=tool_calls, reasoning_content=reasoning_content
-                    ),
-                    index=0,
-                    finish_reason=finish_reason,
-                )
-            ],
+            choices=[ChoiceChunk(delta=delta, index=0, finish_reason=finish_reason)],
             usage=usage,
             system_fingerprint="",
             object="chat.completion.chunk",