diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index 52f2783a82f..bc6f8ccc5a2 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -2115,10 +2115,9 @@ async def async_data_generator(response, user_api_key_dict):
     try:
         start_time = time.time()
         async for chunk in response:
-            verbose_proxy_logger.debug(f"returned chunk: {chunk}")
-            assert isinstance(chunk, litellm.ModelResponse)
+            chunk = chunk.model_dump_json(exclude_none=True)
             try:
-                yield f"data: {json.dumps(chunk.model_dump(exclude_none=True))}\n\n"
+                yield f"data: {chunk}\n\n"
             except Exception as e:
                 yield f"data: {str(e)}\n\n"
 
diff --git a/litellm/utils.py b/litellm/utils.py
index 6bc229e96ee..d8986be6bb2 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -205,18 +205,18 @@ def map_finish_reason(
 
 class FunctionCall(OpenAIObject):
     arguments: str
-    name: str
+    name: Optional[str] = None
 
 
 class Function(OpenAIObject):
     arguments: str
-    name: str
+    name: Optional[str] = None
 
 
 class ChatCompletionDeltaToolCall(OpenAIObject):
-    id: str
+    id: Optional[str] = None
     function: Function
-    type: str
+    type: Optional[str] = None
     index: int
 
 
@@ -275,8 +275,11 @@ class Delta(OpenAIObject):
         super(Delta, self).__init__(**params)
         self.content = content
         self.role = role
-        self.function_call = function_call
-        if tool_calls is not None and isinstance(tool_calls, dict):
+        if function_call is not None and isinstance(function_call, dict):
+            self.function_call = FunctionCall(**function_call)
+        else:
+            self.function_call = function_call
+        if tool_calls is not None and isinstance(tool_calls, list):
             self.tool_calls = []
             for tool_call in tool_calls:
                 if tool_call.get("index", None) is None:
@@ -8727,7 +8730,7 @@ class CustomStreamWrapper:
                         or original_chunk.choices[0].delta.tool_calls is not None
                     ):
                         try:
-                            delta = dict(original_chunk.choices[0].delta)
+                            delta = original_chunk.choices[0].delta
                             model_response.system_fingerprint = (
                                 original_chunk.system_fingerprint
                             )
@@ -8762,7 +8765,9 @@ class CustomStreamWrapper:
                                                 is None
                                             ):
                                                 t.function.arguments = ""
-                            model_response.choices[0].delta = Delta(**delta)
+                            _json_delta = delta.model_dump()
+                            print_verbose(f"_json_delta: {_json_delta}")
+                            model_response.choices[0].delta = Delta(**_json_delta)
                         except Exception as e:
                             traceback.print_exc()
                             model_response.choices[0].delta = Delta()