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77<Note>
8 For how zero data retention (ZDR) applies to this feature, see [API and data retention](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention).
8 To learn how zero data retention (ZDR) applies to this feature, see [API and data retention](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention).
99</Note>
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1111A model that answers in a single pass has to get everything right on the first try: no scratch work, no checking, no changing course halfway through. For a proof, a tricky bug, or a long agentic task, the first approach is often not the best one.
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806806The `thinking` parameter controls whether Claude thinks in [thinking blocks](https://platform.claude.com/docs/en/build-with-claude/thinking) before answering; the `effort` parameter controls how much work Claude puts into the whole response, which in adaptive mode includes how often and how deeply it thinks. Don't pass `adaptive` as an `effort` value: `adaptive` is a thinking mode, not an effort level.
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808For what each effort level does to thinking behavior, see the [per-level thinking behavior table](https://platform.claude.com/docs/en/build-with-claude/thinking-steering-and-cost#effort-levels) on the [Steering thinking](https://platform.claude.com/docs/en/build-with-claude/thinking-steering-and-cost) page. The [Effort](https://platform.claude.com/docs/en/build-with-claude/effort) page documents the parameter itself, including which levels each model supports. On Claude Opus 4.5, the only extended-thinking-only model that supports effort, effort composes with `budget_tokens`. See [Budget rules and tuning](https://platform.claude.com/docs/en/build-with-claude/extended-thinking#budget-rules-and-tuning).
808To learn what each effort level does to thinking behavior, see the [per-level thinking behavior table](https://platform.claude.com/docs/en/build-with-claude/thinking-steering-and-cost#effort-levels) on the [Steering thinking](https://platform.claude.com/docs/en/build-with-claude/thinking-steering-and-cost) page. The [Effort](https://platform.claude.com/docs/en/build-with-claude/effort) page documents the parameter itself, including which levels each model supports. On Claude Opus 4.5, the only extended-thinking-only model that supports effort, effort composes with `budget_tokens`. See [Budget rules and tuning](https://platform.claude.com/docs/en/build-with-claude/extended-thinking#budget-rules-and-tuning).
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810810With the two controls separated this way, pick the one that matches your goal:
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10051005When continuing a conversation on the same model, pass each thinking block back to the API exactly as received, including blocks whose `thinking` field is empty. Don't edit or reconstruct them. Reading the summary text for display is fine: the API rejects blocks whose returned content has been modified, not blocks you have read. Text placed in an empty omitted `thinking` field is [ignored rather than rejected](https://platform.claude.com/docs/en/build-with-claude/thinking#controlling-thinking-display).
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1007For how thinking blocks are handled when you switch models mid-conversation, see [Thinking block preservation by model](https://platform.claude.com/docs/en/build-with-claude/thinking#thinking-block-preservation-by-model).
1007To learn how thinking blocks are handled when you switch models mid-conversation, see [Thinking block preservation by model](https://platform.claude.com/docs/en/build-with-claude/thinking#thinking-block-preservation-by-model).
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10091009Two exceptions, covered in [Fallback credit](https://platform.claude.com/docs/en/build-with-claude/fallback-credit):
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