Glossary · Phase 10 · Agent harnesses
Stop reason
The field in each Messages API reply that says why the model stopped, such as end_turn, tool_use or max_tokens. The loop branches on it.
Try it now
Watch delay double after each temporary error. The 200 ends the loop, so the third wait never happens.
Learn it properly
The core loop, built properly · Stop reasons, parallel tool calls, errors and turn budgets. About 35 minutes.
Other terms from the same lesson
- append-only: Only ever adding to the end, never editing what's there. Agent transcripts and session logs work this way.
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