fast-mode changedbuild-with-claude/fast-mode
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## Supported models and platforms ## Supported models
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1414 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).
1515</Note>
1616
17## Supported models
17## Supported models and platforms
1818
19Fast mode is supported on the following models:
19Fast mode is supported on the following models and platforms:
2020
21* Claude Opus 5.5 (claude-opus-5-5)
22* Claude Opus 5 (claude-opus-5)
23* Claude Opus 4.8 (claude-opus-4-8)
21| Supported model | Supported platforms |
22| --------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
23| Claude Opus 5.5 (claude-opus-5-5) | Claude API, including [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview)<br />[Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), for deployments hosted on Azure |
24| Claude Opus 5 (claude-opus-5) | Claude API, including [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview) |
25| Claude Opus 4.8 (claude-opus-4-8) | Claude API, including [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview) |
2426
25<Note>
26 Fast mode is available on the Claude API, including [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview). Fast mode for Claude Opus 5.5 is also available on [Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry) for deployments hosted on Azure, but not for deployments hosted on Anthropic. Fast mode is not available on Amazon Bedrock, Claude Platform on AWS, or Google Cloud.
27</Note>
27If you were using fast mode on an earlier model, [migrate to a model that supports fast mode](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide).
2828
29<Note>
30 Fast mode is not available on Claude Opus 4.7. Requests to `claude-opus-4-7` with `speed: "fast"` return an error; unlike Claude Opus 4.6 (see the following note), requests do not fall back to standard speed. The model itself remains available at standard speed. To continue using fast mode, see [Migrating to Claude Opus 5.5 from Claude Opus 4.7](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#migrating-from-claude-opus-47).
31</Note>
29Fast mode is not available for Claude in Microsoft Foundry deployments [hosted on Anthropic](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#hosting-options).
3230
33<Note>
34 Fast mode is not available on Claude Opus 4.6. Requests to `claude-opus-4-6` that set `speed` need the `fast-mode-2026-02-01` beta header; without it, they return a `400` error. With the header, requests with `speed: "fast"` run at standard speed and are billed at [standard rates](https://platform.claude.com/docs/en/about-claude/pricing) rather than fast mode's premium rates, and the response reports [`usage.speed: "standard"`](https://platform.claude.com/docs/en/build-with-claude/fast-mode#checking-which-speed-was-used). To continue using fast mode, see [Migrating to Claude Opus 5.5 from Claude Opus 4.6 and earlier Opus models](https://platform.claude.com/docs/en/models/opus-5-5/migration-guide#migrating-from-claude-opus-46).
35</Note>
36
3731## How fast mode works
3832
3933Fast mode runs the same model with a faster inference configuration. There is no change to intelligence or capabilities.
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185179 );
186180
187181 foreach ($response->content as $block) {
188 if ($block->type === 'text') {
182 if ($block instanceof \Anthropic\Messages\TextBlock) {
189183 echo $block->text, PHP_EOL;
190184 }
191185 }
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227221
228222Fast 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.
229223
230Claude Opus 5.5 has a default fast mode rate limit in every [usage tier](https://platform.claude.com/docs/en/api/rate-limits), so you don't need to request access to use fast mode with it.
224Claude 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.
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232226The response includes headers that indicate your fast mode rate limit status:
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244238
245239## Checking which speed was used
246240
247The 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: a request with `speed: "fast"` and the `fast-mode-2026-02-01` beta header does not return an error but runs at standard speed, and `usage.speed` shows `"standard"`. Without the header, the request returns a `400` error.
241The 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-and-platforms) 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.
248242
249243<CodeGroup>
250244 ```bash cURL
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395389
396390### Falling back to standard speed
397391
398<Note>
399 This section covers an opt-in client-side fallback when fast mode is rate limited. It is separate from the behavior on [Claude Opus 4.6](https://platform.claude.com/docs/en/build-with-claude/fast-mode#supported-models), where fast mode is not available.
400</Note>
401
402392If 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, java, php: `maxRetries`; csharp: `MaxRetries`; go: `option.WithMaxRetries`) to `0` on the initial fast request to skip automatic retries and fail immediately on rate limit errors.
403393
404394<Note>
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731721## Considerations
732722
733723* **Prompt caching:** Switching between fast and standard speed invalidates the prompt cache. Requests at different speeds do not share cached prefixes.
734* **Supported models:** Fast mode is supported on Claude Opus 5.5, Claude Opus 5, and Claude Opus 4.8. See [Supported models](https://platform.claude.com/docs/en/build-with-claude/fast-mode#supported-models).
735724* **TTFT:** Fast mode's benefits are focused on output tokens per second (OTPS), not time to first token (TTFT).
736725* **Batch API:** Fast mode is not available with the [Batch API](https://platform.claude.com/docs/en/build-with-claude/batch-processing).
737726* **Priority Tier:** Fast mode is not available with a [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers) commitment.
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