microsoft/semantic-kernel · error · AgentThreadOperationException

The thread is not a Copilot Studio Agent thread.

Error message

The thread is not a Copilot Studio Agent thread.

What it means

Raised by CopilotStudioAgent.get_response() after _ensure_thread_exists_with_messages returns a thread that is not an instance of CopilotStudioAgentThread. The method passes expected_type=CopilotStudioAgentThread to the thread-resolution helper, but if the caller supplies a pre-existing thread of a different concrete type (e.g. ChatHistoryAgentThread), the isinstance check fails. It is an AgentThreadOperationException.

Source

Thrown at python/semantic_kernel/agents/copilot_studio/copilot_studio_agent.py:442

        Args:
            messages: The messages to send to the agent.
            thread: The thread to use for the agent.
            arguments: The arguments to pass to the agent. These take precedence over the agent-defined args.
            kernel: The kernel to use for the agent. This kernel takes precedence over the agent-defined kernel.
            **kwargs: Additional keyword arguments.

        Returns:
            A chat message content and thread with the response.
        """
        thread = await self._ensure_thread_exists_with_messages(
            messages=messages,
            thread=thread,
            construct_thread=lambda: CopilotStudioAgentThread(self.client),
            expected_type=CopilotStudioAgentThread,
        )
        if not isinstance(thread, CopilotStudioAgentThread):
            raise AgentThreadOperationException("The thread is not a Copilot Studio Agent thread.")

        normalized_messages = self._normalize_messages(messages)

        responses: list[ChatMessageContent] = []
        async for response in self._inner_invoke(
            thread=thread,
            messages=normalized_messages,
            on_intermediate_message=None,
            arguments=arguments,
            kernel=kernel,
            **kwargs,
        ):
            responses.append(response)

        return AgentResponseItem(message=responses[-1], thread=thread)

    @trace_agent_invocation
    @override

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Omit the thread argument so the agent creates its own CopilotStudioAgentThread internally.
2. Pass an explicit CopilotStudioAgentThread(agent.client) when you need to control the thread lifecycle.
3. Keep per-agent-type thread instances; do not mix thread types across agent implementations.

Example fix

# before
thread = ChatHistoryAgentThread()
await copilot_agent.get_response("hello", thread=thread)  # raises

# after
thread = CopilotStudioAgentThread(copilot_agent.client)
await copilot_agent.get_response("hello", thread=thread)

from semantic_kernel.agents.copilot_studio.copilot_studio_agent import CopilotStudioAgentThread

def is_copilot_thread(t) -> bool:
    return isinstance(t, CopilotStudioAgentThread)

from semantic_kernel.exceptions.agent_exceptions import AgentThreadOperationException

if thread is not None and not isinstance(thread, CopilotStudioAgentThread):
    thread = CopilotStudioAgentThread(agent.client)
await agent.get_response("hello", thread=thread)

When it happens

Trigger: Calling agent.get_response(messages, thread=some_other_thread) where some_other_thread is a plain AgentThread, ChatHistoryAgentThread, or any other AgentThread subclass that is not CopilotStudioAgentThread.

Common situations: Sharing a thread across different agent types in a multi-agent pipeline; passing a thread created for a ChatCompletionAgent to a CopilotStudioAgent by mistake; refactoring code that previously used a different agent type.

Related errors

• {self.__class__.__name__} currently only supports agent thre
• CopilotClient cannot be None
• Cannot create a thread that has been deleted.
• Cannot delete the thread, since it has not been created.
• This method is not implemented for CopilotStudioAgent. Messa

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/0ec15cc49e7eedf7. Report an issue: GitHub.