Support NativeOutput with FunctionModel (#2843)

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: Douwe Maan <[email protected]>

Author: DouweM

pydantic_ai_slim/pydantic_ai/models/function.py

@@ -31,7 +31,7 @@
     UserContent,
     UserPromptPart,
 )
-from ..profiles import ModelProfileSpec
+from ..profiles import ModelProfile, ModelProfileSpec
 from ..settings import ModelSettings
 from ..tools import ToolDefinition
 from . import Model, ModelRequestParameters, StreamedResponse
@@ -111,6 +111,12 @@ def __init__(
         stream_function_name = self.stream_function.__name__ if self.stream_function is not None else ''
         self._model_name = model_name or f'function:{function_name}:{stream_function_name}'
 
+        # Use a default profile that supports JSON schema and object output if none provided
+        if profile is None:
+            profile = ModelProfile(
+                supports_json_schema_output=True,
+                supports_json_object_output=True,
+            )
         super().__init__(settings=settings, profile=profile)
 
     async def request(

tests/test_agent.py

@@ -1557,7 +1557,7 @@ def return_city_location(messages: list[ModelMessage], _info: AgentInfo) -> Mode
             text = '{"city": "Mexico City", "country": "Mexico"}'
         return ModelResponse(parts=[TextPart(content=text)])
 
-    m = FunctionModel(return_city_location, profile=ModelProfile(supports_json_schema_output=True))
+    m = FunctionModel(return_city_location)
 
     class CityLocation(BaseModel):
         city: str