One read of Claude Developer Platformapi-20261015T200735Z
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76-78 of 78, page 4 of 4This capture is too large to show at once. Changes 76-78 of 78 are below, significant first; the rest are on the following screens.
models/opus-5-5/migration-guide Changed · +2 / -2 lines
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309309* Remove any context-window beta header.
310310* If you rebuild conversation history to update instructions, consider switching to a mid-conversation system message to preserve prompt cache hits.
311311* Verify your stop-reason handling reads `stop_details` on refusals.
312* If you want fast mode, which Claude Opus 4.7 rejects, set `speed: "fast"` with the `fast-mode-2026-02-01` beta header on the Claude API.
312* If you want fast mode, which Claude Opus 4.7 rejects, set `speed: "fast"` on your Claude API requests. Claude Opus 5.5 doesn't need a beta header.
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314314### Claude Opus 4.6 or earlier
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12041204
120512054. **Refusal stop details:** When the model declines a request, Claude Opus 5.5 returns a `stop_details` object that names the category of refusal, alongside the `refusal` stop reason. Claude Opus 4.7 returns the same object, so this matters only if your stop-reason handling does not read it yet. No beta header is required, and there is no opt-out. If your stop-reason handling doesn't read it yet, see [Handling stop reasons](https://platform.claude.com/docs/en/build-with-claude/handling-stop-reasons). Claude Opus 5.5 declines in more categories; see [Safety classifiers and fallback](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#safety-classifiers-and-fallback).
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12075. **Fast mode:** Claude Opus 5.5 supports [fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) (research preview) on the Claude API. Fast mode is not available on Claude Opus 4.7, where requests with `speed: "fast"` return an error. Set `speed: "fast"` with the `fast-mode-2026-02-01` beta header.
12075. **Fast mode:** Claude Opus 5.5 supports [fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) on the Claude API. Fast mode is not available on Claude Opus 4.7, where requests with `speed: "fast"` return an error. Set `speed: "fast"` on your requests. Claude Opus 5.5 doesn't need a beta header.
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120912096. **Computer use toolset and browser use tool:** On the Claude API and Google Cloud, Claude Opus 5.5 supports [computer use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/computer-use-tool) as the `computer_toolset_20260801` toolset and the [browser use tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool) for tasks inside webpages. Claude Opus 4.7 supports neither. On those platforms Claude Opus 5.5 doesn't accept the earlier `computer_20251124` tool; see the [computer use breaking change](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#computer-use-toolset).
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models/opus-5-5/overview Changed · +1 / -1 lines
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108108 </Card>
109109
110110 <Card title="Fast mode" icon="lightning" href="https://platform.claude.com/docs/en/build-with-claude/fast-mode">
111 Lower-latency Claude Opus 5.5 on the Claude API (research preview), priced separately.
111 Lower-latency Claude Opus 5.5 on the Claude API, priced separately.
112112 </Card>
113113</CardGroup>
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models/opus-5-5/whats-new-opus-5-5 Changed · +1 / -1 lines
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6464
6565### Fast mode
6666
67[Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) (research preview) is available for Claude Opus 5.5 on the Claude API only; it is not available on Amazon Bedrock, Claude Platform on AWS, Google Cloud, or Microsoft Foundry. Set `speed: "fast"` with the `fast-mode-2026-02-01` beta header. See [Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) for access, supported models, and pricing.
67[Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) is available for Claude Opus 5.5 on the Claude API only; it is not available on Amazon Bedrock, Claude Platform on AWS, Google Cloud, or Microsoft Foundry. On the Claude API, set `speed: "fast"` on your request. Claude Opus 5.5 doesn't need a beta header. See [Fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode) for supported models, rate limits, and pricing.
6868
6969### Define tools in a message (beta)
7070