_rstrip_last_assistant_message only strips trailing whitespace from the content — it does not remove the assistant message.

[shivase]

What happened?

Describe the bug
_rstrip_last_assistant_message only strips trailing whitespace from the content — it does not remove the assistant message. So when the message history genuinely ends with a non-empty assistant message, it passes through unchanged and Anthropic rejects it.

Claude Recommend Fix

        from autogen_ext.models.anthropic import AnthropicChatCompletionClient

        class _AnthropicClient(AnthropicChatCompletionClient):
            # autogen-ext 0.7.x only whitespace-strips trailing assistant messages;
            # Anthropic API requires the conversation to end with a user message.
            def _rstrip_last_assistant_message(self, messages: Sequence[_LLMMessage]) -> Sequence[_LLMMessage]:
                msgs = list(messages)
                while msgs and isinstance(msgs[-1], _AssistantMessage):
                    msgs.pop()
                return msgs

        return _AnthropicClient(
            model=model_name,
            api_key=llm_key,
        )

Which packages was the bug in?

Python Extensions (autogen-ext)

AutoGen library version.

Python 0.7.5

Other library version.

No response

Model used

anthropic/claude-sonnet-4-6

Model provider

Anthropic

Other model provider

No response

Python version

None

.NET version

None

Operating system

None