Fix StreamedResponse.model_name for Azure OpenAI (#2945)

Author: DouweM

pydantic_ai_slim/pydantic_ai/models/openai.py

@@ -586,9 +586,12 @@ async def _process_streamed_response(
                 'Streamed response ended without content or tool calls'
             )
 
+        # ChatCompletionChunk.model is required to be set, but Azure OpenAI omits it so we fall back to the model name set by the user.
+        model_name = first_chunk.model or self._model_name
+
         return OpenAIStreamedResponse(
             model_request_parameters=model_request_parameters,
-            _model_name=first_chunk.model,
+            _model_name=model_name,
             _model_profile=self.profile,
             _response=peekable_response,
             _timestamp=number_to_datetime(first_chunk.created),

tests/models/test_openai.py

@@ -397,8 +397,11 @@ async def test_stream_text(allow_model_requests: None):
 
 
 async def test_stream_text_finish_reason(allow_model_requests: None):
+    first_chunk = text_chunk('hello ')
+    # Test that we fall back to the model name set by the user if the model name is not set in the first chunk, like on Azure OpenAI.
+    first_chunk.model = ''
     stream = [
-        text_chunk('hello '),
+        first_chunk,
         text_chunk('world'),
         text_chunk('.', finish_reason='stop'),
     ]
@@ -418,7 +421,7 @@ async def test_stream_text_finish_reason(allow_model_requests: None):
                     ModelResponse(
                         parts=[TextPart(content='hello world.')],
                         usage=RequestUsage(input_tokens=6, output_tokens=3),
-                        model_name='gpt-4o-123',
+                        model_name='gpt-4o',
                         timestamp=IsDatetime(),
                         provider_name='openai',
                         provider_details={'finish_reason': 'stop'},