fast-mode changedbuild-with-claude/fast-mode
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## Supported platforms ## Model availability ### Claude Opus 5.5 ### Claude Opus 5 and Claude Opus 4.8 ## Retries and fallbacks ## Supported models and platforms ## Retries and fallback
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22title: Fast mode
33url: https://platform.claude.com/docs/en/build-with-claude/fast-mode
44description: Get up to 2.5x higher output tokens per second from supported Claude models.
5featureMetadata:
6 zdr:
7 eligibility: eligible
8 note: Excludes [Covered Models](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention#model-specific-data-retention-requirements).
9 supportedModels:
10 - claude-opus-5-5
11 - claude-opus-5
12 - claude-opus-4-8
13 supportedPlatforms:
14 Claude API:
15 availability: ga
16 note: Includes [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview).
17 Microsoft Foundry:
18 availability: ga
19 note: Available for Claude Opus 5.5 on deployments hosted on Azure, not on deployments [hosted on Anthropic](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#hosting-options).
20 details:
21 - 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.
522---
623
7Fast mode delivers up to 2.5x higher output tokens per second from Claude Opus 5.5, Claude Opus 5, and Claude Opus 4.8 at premium pricing. Set `speed: "fast"` on your request to opt in.
24Fast 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.
825
9<Note>
10 Fast mode for Claude Opus 5.5 doesn't need the `fast-mode-2026-02-01` beta header or an access request. Requests that still send the header keep working. Fast mode for Claude Opus 5 and Claude Opus 4.8 is in research preview: contact your account manager or [join the waitlist](https://claude.com/fast-mode) to request access, and send the [beta header](https://platform.claude.com/docs/en/api/beta-headers) on your requests.
11</Note>
12
13<Note>
14 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).
15</Note>
16
17## Supported models and platforms
18
19Fast mode is supported on the following models and platforms:
20
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) |
26
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).
28
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).
30
3126## How fast mode works
3227
3328Fast mode runs the same model with a faster inference configuration. There is no change to intelligence or capabilities.
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3429
3530* Up to 2.5x higher output tokens per second compared to standard speed
3631* Speed benefits are focused on output tokens per second (OTPS), not time to first token (TTFT)
37* Same model weights and behavior (not a different model)
3832* Compatible with [streaming](https://platform.claude.com/docs/en/build-with-claude/streaming), where the OTPS gain is most visible
3933
4034## Basic usage
4135
42Models in research preview also need the `fast-mode-2026-02-01` [beta header](https://platform.claude.com/docs/en/api/beta-headers).
36Fast mode works only on supported models. See [Model availability](https://platform.claude.com/docs/en/build-with-claude/fast-mode#supported-models) for details, including which models need a beta header.
4337
4438<CodeGroup>
4539 ```bash cURL
from line 195
201195 ```
202196</CodeGroup>
203197
198## Supported platforms
199
200Fast mode is available on the Claude API, including [Claude Managed Agents](https://platform.claude.com/docs/en/managed-agents/overview).
201
202Fast mode on 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. It is not available for deployments [hosted on Anthropic](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#hosting-options).
203
204## Model availability
205
206Fast mode is available only on the following models. If 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).
207
208### Claude Opus 5.5
209
210Fast mode is available on Claude Opus 5.5. It doesn't need a beta header or an access request.
211
212### Claude Opus 5 and Claude Opus 4.8
213
214Fast mode on Claude Opus 5 and Claude Opus 4.8 is in research preview. Requests that set `speed` must send the `fast-mode-2026-02-01` [beta header](https://platform.claude.com/docs/en/api/beta-headers); without it, they return a `400` error. To access fast mode on Claude Opus 5 or Claude Opus 4.8, contact your account manager or [join the waitlist](https://claude.com/fast-mode).
215
204216## Pricing
205217
206Fast mode is priced at a multiplier on standard rates across the full context window, including requests over 200k input tokens. The following table shows fast mode pricing for the supported models:
218Fast mode is priced at a multiplier on standard rates across the full context window, including requests over 200k input tokens.
207219
208220| Model | Input | Output |
209221| ------------------------------- | -------------- | -------------- |
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238250
239251## Checking which speed was used
240252
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.
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.
242254
243255<CodeGroup>
244256 ```bash cURL
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255267 ```
256268
257269 ```bash CLI
258 ant messages create \
259 --transform usage.speed \
260 --raw-output <<'YAML'
270 ant messages create <<'YAML'
261271 model: claude-opus-5-5
262272 max_tokens: 1024
263273 speed: fast
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381391
382392To track fast mode usage and costs across your organization, see the [Usage and Cost API](https://platform.claude.com/docs/en/manage-claude/usage-cost-api).
383393
384## Retries and fallback
394## Retries and fallbacks
385395
386396### Automatic retries
387397
388When fast mode rate limits are exceeded, the API returns a `429` error with a `retry-after` header. The SDK automatically retries these requests up to 2 times by default (configurable with `max_retries` (typescript, java, php: `maxRetries`; csharp: `MaxRetries`; go: `option.WithMaxRetries`)), waiting for the server-specified delay before each retry. Because fast mode uses continuous token replenishment, the `retry-after` delay is typically short and requests succeed once capacity is available.
398The SDK automatically retries fast mode `429` errors up to 2 times by default (configurable with `max_retries` (typescript, java, php: `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.
389399
390400### Falling back to standard speed
391401
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397407
398408Because setting `max_retries` (typescript, java, php: `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.
399409
400<CodeGroup exclude="shell:cURL">
401 ```bash CLI
402 # `ant` retries 429/5xx automatically and has no per-request max_retries
403 # override, so on a fast-mode 429 the fallback runs after the built-in
404 # retries exhaust. --transform-error surfaces error.type for branching.
405 create_message_with_fast_fallback() {
406 local speed="$1" max_attempts="${2:-3}" body out
407 body=${3:-$(cat)}
408 out=$(
409 ant messages create \
410 ${speed:+--speed "$speed"} \
411 --transform-error error.type --format-error yaml <<<"$body" 2>/dev/null
412 ) && { printf '%s\n' "$out"; return; }
413 case "$out" in
414 rate_limit_error)
415 if [[ -n "$speed" ]]; then
416 create_message_with_fast_fallback "" "$max_attempts" "$body"
417 return
418 fi ;;
419 overloaded_error | api_error | "")
420 if (( max_attempts > 1 )); then
421 create_message_with_fast_fallback "$speed" $((max_attempts - 1)) "$body"
422 return
423 fi ;;
424 esac
425 printf '%s\n' "${out:-connection_error}" >&2
426 return 1
427 }
428
429 MESSAGE=$(
430 create_message_with_fast_fallback fast <<'YAML'
431 model: claude-opus-5-5
432 max_tokens: 1024
433 messages:
434 - role: user
435 content: Hello
436 YAML
437 )
438 ```
439
410<CodeGroup exclude="shell:cURL, shell:CLI">
440411 ```python Python
441412 client = anthropic.Anthropic()
442413
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720691
721692## Considerations
722693
723* **Prompt caching:** Switching between fast and standard speed invalidates the prompt cache. Requests at different speeds do not share cached prefixes.
724* **TTFT:** Fast mode's benefits are focused on output tokens per second (OTPS), not time to first token (TTFT).
725694* **Batch API:** Fast mode is not available with the [Batch API](https://platform.claude.com/docs/en/build-with-claude/batch-processing).
726695* **Priority Tier:** Fast mode is not available with a [Priority Tier](https://platform.claude.com/docs/en/api/service-tiers) commitment.
727* **Claude Platform on AWS:** Fast mode is not currently available on [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws).
728696
729697## Next steps
730698
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