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2828<Note>
2929 Claude Fable 5.1 runs safety classifiers and can return `stop_reason: "refusal"`. See [Refusals, fallback, and billing](https://platform.claude.com/docs/en/models/fable-5-1/whats-new-fable-5-1#refusals-fallback-and-billing) and [Reduce safeguard false positives](https://platform.claude.com/docs/en/build-with-claude/prompt-engineering/prompting-claude-fable-5-1#reduce-safeguard-false-positives).
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31 Prompts, skills, and tool descriptions that ask the model to write out its thinking or reasoning may be declined with the `reasoning_extraction` category. Ask for a short explanation or a summary of the actions taken instead, or read the reasoning from [summarized thinking](https://platform.claude.com/docs/en/build-with-claude/thinking#summarized-thinking) blocks (`display: "summarized"`). See [Keep reasoning in thinking blocks](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#keep-reasoning-in-thinking-blocks).
3032</Note>
3133
3234## Consider all effort levels
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