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19161916On a refusal, the `stop_details` object identifies the policy category that triggered it. The categories and the full refusal response shape are covered on [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response). `stop_details` is `null` for all stop reasons other than `refusal`.
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1918A refused request on Claude Fable 5 or Claude Opus 5 can usually be served by retrying on another Claude model, and [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback) shows how to set up that retry, server-side or in your client. [Fallback credit](https://platform.claude.com/docs/en/build-with-claude/fallback-credit) covers how to avoid paying the prompt-cache cost twice when you build the retry yourself.
1918A refused request on Claude Fable 5.1, Claude Fable 5, or Claude Opus 5 can usually be served by retrying on another Claude model. [Refusals and fallback](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback) shows how to set up that retry, server-side or in your client. If you build the retry yourself from Claude Fable 5.1, Claude Fable 5, or Claude Opus 5, [fallback credit](https://platform.claude.com/docs/en/build-with-claude/fallback-credit) covers how to avoid paying the prompt-cache cost twice.
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19201920### model\_context\_window\_exceeded
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