microsoft/autogen · error · ValueError

Model does not support JSON output

Error message

Model does not support JSON output

What it means

Error "Model does not support JSON output" thrown in microsoft/autogen.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py:576

        json_output: Optional[bool | type[BaseModel]] = None,
        extra_create_args: Mapping[str, Any] = {},
        cancellation_token: Optional[CancellationToken] = None,
    ) -> CreateResult:
        # Copy create args and update with extra args
        create_args = self._create_args.copy()
        create_args.update(extra_create_args)

        # Check for vision capability if images are present
        if self.model_info["vision"] is False:
            for message in messages:
                if isinstance(message, UserMessage):
                    if isinstance(message.content, list) and any(isinstance(x, Image) for x in message.content):
                        raise ValueError("Model does not support vision and image was provided")

        # Handle JSON output format
        if json_output is not None:
            if self.model_info["json_output"] is False and json_output is True:
                raise ValueError("Model does not support JSON output")

            if json_output is True:
                create_args["response_format"] = {"type": "json_object"}
            elif isinstance(json_output, type):
                raise ValueError("Structured output is currently not supported for Anthropic models")

        # Process system message separately
        system_message = None
        anthropic_messages: List[MessageParam] = []

        # Merge continuous system messages into a single message
        messages = self._merge_system_messages(messages)
        messages = self._rstrip_last_assistant_message(messages)

        for message in messages:
            if isinstance(message, SystemMessage):
                if system_message is not None:
                    # if that case, system message is must only one

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Disable json_output or choose a model supporting it

Example fix

Set json_output=False or use a json-capable model

When it happens

Trigger: Thrown at python/packages/autogen-ext/src/autogen_ext/models/anthropic/_anthropic_client.py:576 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/f6042c8d98c2a393. Report an issue: GitHub.