NousResearch/hermes-agent · error · EmptyStreamError

Provider returned an empty stream with no stop_reason (possi

Error message

Provider returned an empty stream with no stop_reason (possible upstream error or malformed event stream).

What it means

Error "Provider returned an empty stream with no stop_reason (possible upstream error or malformed event stream)." thrown in NousResearch/hermes-agent.

Source

Thrown at agent/chat_completion_helpers.py:4051

            before the drop it additionally rides the bounded stream-retry
            the eventless case uses (probe-verified recovery), while a
            drop after streamed preamble text degrades to the
            partial-stream-stub/continuation path instead — still never an
            empty-args execution.
            """
            if getattr(message, "stop_reason", None) is not None:
                return False
            for block in getattr(message, "content", None) or []:
                if getattr(block, "type", None) == "tool_use":
                    return True
            return False

        if (
            base_final_message is not None
            and not getattr(base_final_message, "content", None)
            and getattr(base_final_message, "stop_reason", None) is None
        ):
            raise EmptyStreamError(
                "Provider returned an empty stream with no stop_reason "
                "(possible upstream error or malformed event stream)."
            )
        if base_final_message is not None and not stream.output_modified:
            if _tool_use_dropped_mid_stream(base_final_message):
                raise EmptyStreamError(
                    "Stream ended with no stop_reason while a tool_use "
                    "block was still incomplete; treating as a "
                    "mid-tool-call stream drop (#80498)."
                )
            return base_final_message
        final_message = accumulator.response(base_final_message)
        if (
            not getattr(final_message, "content", None)
            and getattr(final_message, "stop_reason", None) is None
        ):
            raise EmptyStreamError(
                "Provider returned an empty stream with no stop_reason "

View on GitHub (pinned to c896c09c42)

Solutions

1. Retry the call; the stream ended without a stop_reason, typically an upstream error.
2. Reduce request size or max_tokens if the provider truncates the stream.
3. Check provider logs/status for malformed streaming responses.

When it happens

Trigger: Thrown at agent/chat_completion_helpers.py:4051 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of NousResearch/hermes-agent@c896c09c42 (2026-08-14). Data as JSON: /api/errors/be195cdd96d93286. Report an issue: GitHub.