fast-mode changedbuild-with-claude/fast-mode
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1414 supportedPlatforms:
1515 Claude API: stable
1616 Claude Models on Google Cloud (Anthropic managed): stable
17 Microsoft Foundry (hosted on Azure): stable
17 Microsoft Foundry (hosted on Azure):
18 availability: stable
19 note: On Microsoft Foundry, fast mode is a separate model whose ID ends in `-fast`. Send requests to a deployment of that model, and leave out `speed`.
1820 details:
1921 - Fast mode on Claude Opus 5 and Claude Opus 4.8 is in research preview and needs the `fast-mode-2026-02-01` beta header.
2022---
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2426* **Messages API**: Set `speed: "fast"` on the request.
2527* **Managed Agents**: Set `speed` on the agent’s model object, for example `{"id": "claude-opus-5-5", "speed": "fast"}`.
2628
27Fast mode delivers up to 2.5x higher output tokens per second at premium pricing. Set `speed: "fast"` on your request to opt in. Fast mode is available on Claude Opus 5.5 and in research preview on Claude Opus 5 and Claude Opus 4.8.
29Fast mode delivers up to 2.5x higher output tokens per second at premium pricing. Set `speed: "fast"` on your request to opt in. Fast mode is available on Claude Opus 5.5. Fast mode for Claude Opus 5 and Claude Opus 4.8 is in research preview.
2830
2931## How fast mode works
3032
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3840
3941Fast mode works only on supported models. See [Availability](https://platform.claude.com/docs/en/build-with-claude/fast-mode#feature-availability) for details, including which models need a beta header.
4042
43On [Claude in Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), fast mode is a separate model, such as `claude-opus-5-5-fast`. Send fast mode requests to a deployment of the fast model, and leave out `speed`. A request that sets `speed` on a deployment of the model without `-fast` returns an error.
44
4145<CodeGroup>
4246 ```bash cURL
4347 curl https://api.anthropic.com/v1/messages \
from line 191
187191 model: Anthropic::Model::CLAUDE_OPUS_5_5,
188192 max_tokens: 4096,
189193 speed: "fast",
190 messages: [{role: "user", content: "Refactor this module to use dependency injection"}]
194 messages: [{ role: "user", content: "Refactor this module to use dependency injection" }]
191195 )
192196
193197 response.content.each do |block|
194 puts block.text if block.type == :text
198 puts block.text if block.is_a?(Anthropic::Models::TextBlock)
195199 end
196200 ```
197201</CodeGroup>
from line 202
198202
199203## Rate limits
200204
201Fast 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.
205Fast mode has a dedicated rate limit that is separate from standard rate limits. When you exceed your fast mode rate limit, the API returns a `429` error with a `retry-after` header that says when capacity is available.
202206
203207Claude 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.
204208
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217221
218222## Checking which speed was used
219223
220The 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#availability-feature-support) 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.
224The 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#feature-availability) 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. In this situation, `usage.speed` shows `"standard"`. 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.
221225
222226<CodeGroup>
223227 ```bash cURL
from line 366
362366
363367### Automatic retries
364368
365The SDK automatically retries fast mode `429` errors up to 2 times by default (configurable with `max_retries` (typescript, php: `maxRetries`; java: `.maxRetries()`; csharp: `MaxRetries`; go: `option.WithMaxRetries()`)), waiting for the delay in the `retry-after` header before each retry. Because fast mode uses continuous token replenishment, the `retry-after` delay is typically short and requests succeed once capacity is available.
369The SDK automatically retries fast mode `429` errors up to two times by default (configurable with `max_retries` (typescript, php: `maxRetries`; java: `.maxRetries()`; csharp: `MaxRetries`; go: `option.WithMaxRetries()`)), waiting for the delay in the `retry-after` header before each retry. Because fast mode uses continuous token replenishment, the `retry-after` delay is typically short and requests succeed once capacity is available.
366370
367371### Falling back to standard speed
368372
369If 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.
373If 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"`. On Claude in Microsoft Foundry, the deployment sets the speed, so retry on a deployment of the model without `-fast` instead. 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.
370374
371375<Note>
372376 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.
373377</Note>
374378
375Because setting `max_retries` (typescript, php: `maxRetries`; java: `.maxRetries()`; csharp: `MaxRetries`; go: `option.WithMaxRetries()`) to `0` also disables retries for other transient errors (overloaded, internal server errors), the following examples reissue the original request with default retries for those cases.
379Because setting `max_retries` (typescript, php: `maxRetries`; java: `.maxRetries()`; csharp: `MaxRetries`; go: `option.WithMaxRetries()`) to `0` also disables retries for other transient errors (overloaded, internal server errors), the following examples resend the request after those errors.
376380
377381<CodeGroup exclude="shell:cURL, shell:CLI">
378382 ```python Python
from line 595
591595 use Anthropic\Core\Exceptions\APIConnectionException;
592596 use Anthropic\Core\Exceptions\InternalServerException;
593597 use Anthropic\Core\Exceptions\RateLimitException;
598 use Anthropic\Messages\Model;
594599 use Anthropic\RequestOptions;
595600 // ...
596601 $client = new Client();
from line 630
625630 $message = createMessageWithFastFallback(
626631 $client,
627632 [
628 'model' => 'claude-opus-5-5',
633 'model' => Model::CLAUDE_OPUS_5_5,
629634 'maxTokens' => 1024,
630635 'messages' => [['role' => 'user', 'content' => 'Hello']],
631636 'speed' => 'fast',
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650655
651656 message = create_message_with_fast_fallback(
652657 client,
653 model: "claude-opus-5-5",
658 model: Anthropic::Model::CLAUDE_OPUS_5_5,
654659 max_tokens: 1024,
655660 messages: [{ role: "user", content: "Hello" }],
656661 speed: "fast",
from line 704
699704* Availability: Available
700705* Usage: Set `speed: "fast"` on the request.
701706
702| Status | Cloud platforms | Models |
703| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------ |
704| Available | Claude API, [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed), [Microsoft Foundry (hosted on Azure)](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry) | [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview) |
705| Research preview | Claude API | [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview), [Claude Opus 4.8](https://platform.claude.com/docs/en/models/opus-4-8/overview) |
707| Status | Cloud platforms | Models |
708| --------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------ |
709| Available | Claude API, [Claude Models on Google Cloud (Anthropic managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/anthropic-managed) | [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview) |
710| Available<sup>1</sup> | [Microsoft Foundry (hosted on Azure)](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry) | [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview) |
711| Research preview | Claude API | [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview), [Claude Opus 4.8](https://platform.claude.com/docs/en/models/opus-4-8/overview) |
712
7131. On Microsoft Foundry, fast mode is a separate model whose ID ends in `-fast`. Send requests to a deployment of that model, and leave out `speed`.
706714
707715#### [Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview)
708716
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