fast-mode changedbuild-with-claude/fast-mode
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208208### Claude Opus 5.5
209209
210Fast mode is available on Claude Opus 5.5. It doesn't need a beta header or an access request.
210Fast mode is available on Claude Opus 5.5. It doesn’t need a beta header or an access request.
211211
212212### Claude Opus 5 and Claude Opus 4.8
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234234Fast mode has a dedicated rate limit that is separate from standard Opus rate limits. When your fast mode rate limit is exceeded, the API returns a `429` error with a `retry-after` header indicating when capacity will be available.
235235
236Claude Opus 5.5 has a default fast mode rate limit in the Start, Build, and Scale [usage tiers](https://platform.claude.com/docs/en/api/rate-limits), so you don't need to request access to use fast mode with it. Organizations in the Evaluation tier can use fast mode with Claude Opus 5.5 once they move to the Start, Build, or Scale tier.
236Claude Opus 5.5 has a default fast mode rate limit in the Start, Build, and Scale [usage tiers](https://platform.claude.com/docs/en/api/rate-limits), so you don’t need to request access to use fast mode with it. Organizations in the Evaluation tier can use fast mode with Claude Opus 5.5 once they move to the Start, Build, or Scale tier.
237237
238238The response includes headers that indicate your fast mode rate limit status:
239239
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251251## Checking which speed was used
252252
253The response `usage` object includes a `speed` field that indicates which speed was used, either `"fast"` or `"standard"`. Requesting `speed: "fast"` on a [model that doesn't support fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode#supported-models) returns an error, and so does exceeding fast mode's rate limits or capacity (a `429` or `529`). When a request with `speed: "fast"` succeeds, `usage.speed` is `"fast"`. Claude Opus 4.6 is an exception: instead of returning an error, a request with `speed: "fast"` and the `fast-mode-2026-02-01` beta header succeeds, but runs at standard speed. This behavior is correctly reflected in `usage.speed`, which shows `"standard"` in this situation. On Claude Models on Google Cloud (Anthropic managed), a Claude Opus 4.6 request with `speed: "fast"` returns a `400` error even with the header.
253The response `usage` object includes a `speed` field that indicates which speed was used, either `"fast"` or `"standard"`. Requesting `speed: "fast"` on a [model that doesn’t support fast mode](https://platform.claude.com/docs/en/build-with-claude/fast-mode#supported-models) returns an error, and so does exceeding fast mode’s rate limits or capacity (a `429` or `529`). When a request with `speed: "fast"` succeeds, `usage.speed` is `"fast"`. Claude Opus 4.6 is an exception: instead of returning an error, a request with `speed: "fast"` and the `fast-mode-2026-02-01` beta header succeeds, but runs at standard speed. This behavior is correctly reflected in `usage.speed`, which shows `"standard"` in this situation. On Claude Models on Google Cloud (Anthropic managed), a Claude Opus 4.6 request with `speed: "fast"` returns a `400` error even with the header.
254254
255255<CodeGroup>
256256 ```bash cURL
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400400### Falling back to standard speed
401401
402If you'd prefer to fall back to standard speed rather than wait for fast mode capacity, catch the rate limit error and retry without `speed: "fast"`. Set `max_retries` (typescript, php: `maxRetries`; java: `.maxRetries()`; csharp: `MaxRetries`; go: `option.WithMaxRetries()`) to `0` on the initial fast request to skip automatic retries and fail immediately on rate limit errors.
402If you’d prefer to fall back to standard speed rather than wait for fast mode capacity, catch the rate limit error and retry without `speed: "fast"`. Set `max_retries` (typescript, php: `maxRetries`; java: `.maxRetries()`; csharp: `MaxRetries`; go: `option.WithMaxRetries()`) to `0` on the initial fast request to skip automatic retries and fail immediately on rate limit errors.
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404404<Note>
405405 Falling back from fast to standard speed results in a [prompt cache](https://platform.claude.com/docs/en/build-with-claude/prompt-caching) miss. Requests at different speeds do not share cached prefixes.
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705705 </Card>
706706
707707 <Card title="Pricing" icon="calculator" href="https://platform.claude.com/docs/en/about-claude/pricing#fast-mode-pricing">
708 Learn about Anthropic's pricing structure for models and features.
708 Learn about Anthropic’s pricing structure for models and features.
709709 </Card>
710710
711711 <Card title="Effort" icon="gauge" href="https://platform.claude.com/docs/en/build-with-claude/effort">
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