Messages changedapi/beta/messages
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14 Aug 2026
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39533953 The inference speed mode for this request. `"fast"` enables high output-tokens-per-second inference.
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3955 Some models require the `fast-mode-2026-02-01` beta header for any `speed` value. See [fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode?sdk_languages=http) for which models.
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39553957 - `"standard"`
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39573959 - `"fast"`
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71597161 This is how the tool will be called by the model and in `tool_use` blocks.
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7161 - `allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"`
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7163 - `"direct"`
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7165 - `"code_execution_2
7163 - `allo
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