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fix: override end_turn stop reason when streaming response contains toolUse blocks #1827

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fix: override end_turn stop reason when streaming response contains toolUse blocks #1827

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11 changes: 11 additions & 0 deletions src/strands/event_loop/streaming.py
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Original file line number Diff line number Diff line change
Expand Up @@ -419,6 +419,17 @@ async def process_stream(
elif "redactContent" in chunk:
handle_redact_content(chunk["redactContent"], state)

# Override stop_reason when the model returns "end_turn" but the response
# contains toolUse blocks. Some models (e.g., Sonnet 4.x) can return
# end_turn as stop_reason even when tool calls are present, which prevents
# the event loop from processing those tool calls.
# See: https://github.com/strands-agents/sdk-python/issues/1810
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@pgrayy pgrayy Mar 6, 2026

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Few call outs:

  1. I wouldn't worry about mentioning the ticket here in comments. That is more for the PR itself.
  2. We should try to fix this before the yield ModelStreamChunkEvent above. This way the event is yielded with the correct stop reason.
  3. This I would say warrants a warn instead of a debug.
  4. With this change, we should be able to remove the override logic in https://github.com/strands-agents/sdk-python/blob/main/src/strands/models/bedrock.py#L826.
  5. We should add tests.

if stop_reason == "end_turn":
content = state["message"].get("content", [])
if any("toolUse" in item for item in content):
logger.debug("stop_reason override: end_turn -> tool_use (response contains toolUse blocks)")
stop_reason = "tool_use"

yield ModelStopReason(stop_reason=stop_reason, message=state["message"], usage=usage, metrics=metrics)


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