BoundaryML/baml · error · Exception

BAML Internal error: Stream did not complete successfully…

Error message

BAML Internal error: Stream did not complete successfully. Please report this issue.

What it means

baml_py.stream.get_final_response() raises this generic Exception when a streamed BAML call ends without an exception but also without a result, meaning the stream's internal state machine finished in a neither-success-nor-failure state. The library considers this impossible under normal operation and asks for a bug report.

Solutions

1. Check server/network conditions: retry the request, since a dropped stream can leave no result and no exception.
2. Guard with streaming callbacks to ensure the stream is fully consumed before calling get_final_response().
3. Upgrade baml-py and the BAML CLI to the latest versions — this state may be a fixed engine bug.
4. If reproducible on latest versions, report it (the message explicitly asks for a bug report) with a minimal repro.

Example fix

# before
stream = b.MyFunc.stream(prompt)
result = stream.get_final_response()  # may hit internal error on abrupt stream end

# after
stream = b.MyFunc.stream(prompt)
for partial in stream:
    pass  # fully consume the stream
try:
    result = stream.get_final_response()
except Exception as e:
    result = fallback_completion(prompt)

if not stream.has_pending_items() and stream.get_final_response_cache() is None:
    # stream never produced output; re-issue instead of forcing final response
    stream = client.call.stream(...)

def stream_completed(stream) -> bool:
    try:
        stream.get_final_response()
        return True
    except Exception:
        return False

try:
    result = stream.get_final_response()
except Exception as e:
    if "Stream did not complete successfully" in str(e):
        result = retry_stream(client, prompt)  # re-issue the request
    else:
        raise

When it happens

Trigger: Calling stream.get_final_response() after joining the streaming task when self.__result is None and self.__exception is None — e.g. the async streaming task ended without invoking either the result or error callback.

Common situations: Killed or cancelled stream tasks mid-flight (process interrupts, event-loop shutdown) that bypass both callbacks; engine/FFI bugs in rare partial-response paths; forcing final response on a stream that never started consuming.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• __class_getitem__ for streaming
• getattr(StreamState)
• {message}
• -32603
• -32800

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/92153caf814a6241. Report an issue: GitHub.

Appendix: source

Thrown at engine/language_client_python/python_src/baml_py/stream.py:221

                if done_seen:
                    break
        except Exception as e:
            raise e
        finally:
            if self.__task and self.__task.is_alive():
                self.__task.join(timeout=5.0)

    def get_final_response(self):
        self.__drive_to_completion_in_bg()
        if self.__task is not None:
            self.__task.join()

        if self.__exception is not None:
            raise self.__exception

        if self.__result is None:
            raise Exception(
                "BAML Internal error: Stream did not complete successfully. Please report this issue."
            )

        return self.__final_coerce(self.__result)

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