preserved-thinking changedbuild-with-claude/preserved-thinking
Nearest release: v2.1.284, published an hour after this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
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First seen
1 Sep 2026
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Recorded edits12to this page, all time
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4040Keep sending the full history on every request, thinking blocks included, and let the API drop what the current model can't read. The API never edits your `messages` array, so the dropped blocks stay in your history. When the same history goes back to Claude Fable 5.1, its blocks are readable again, along with the earlier model's thinking. The reasoning is lost for good only if your client removes the blocks itself, for example a harness that strips thinking on a model switch or rebuilds the history from what each model used.
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4444With the `thinking-binding-controls-2026-08-01` [beta header](https://platform.claude.com/docs/en/api/beta-headers), the response lists each dropped block in a top-level `input_transformations` array with `reason: "model_binding_mismatch"`:
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