From ebcf307a2f24e90cc3a22a9cac01df5af3375930 Mon Sep 17 00:00:00 2001
From: Douwe Maan <hi@douwe.me>
Date: Thu, 18 Sep 2025 14:13:36 +0000
Subject: [PATCH] Fix StreamedResponse.model_name for Azure OpenAI

---
 pydantic_ai_slim/pydantic_ai/models/openai.py | 5 ++++-
 tests/models/test_openai.py                   | 7 +++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/pydantic_ai_slim/pydantic_ai/models/openai.py b/pydantic_ai_slim/pydantic_ai/models/openai.py
index 2b83fcad30..f98e24d907 100644
--- a/pydantic_ai_slim/pydantic_ai/models/openai.py
+++ b/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),
diff --git a/tests/models/test_openai.py b/tests/models/test_openai.py
index 3ae08f6898..547c0d72e8 100644
--- a/tests/models/test_openai.py
+++ b/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'},