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Sweep 10 Nov 2026 · 02:18Z Build v2.1.322 539 read Stable v2.1.311 Latest v2.1.322 Next v2.1.322 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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fallback-credit changedbuild-with-claude/fallback-credit

Nearest release: v2.1.321, published under an hour before this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

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First seen 14 Aug 2026 this site's first read of the page
Recorded edits23to this page, all time

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66 status: beta
77 betaHeader: fallback-credit-2026-07-01, server-side-fallback-2026-07-01, fallback-credit-2026-06-01
88 supportedModels:
9 - claude-fable-5-2
10 - claude-mythos-5-2
911 - claude-fable-5-1
1012 - claude-mythos-5-1
1113 - claude-fable-5
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528530 
529531Fallback credit is in beta on the Claude API, Amazon Bedrock, Claude Platform on AWS, Claude Models on Google Cloud (Google managed), and Microsoft Foundry. Refusals in [Message Batches](https://platform.claude.com/docs/en/build-with-claude/batch-processing) don’t mint credit tokens, and redemption applies only to direct Messages API requests: a token passed on a batch request is accepted but ignored. A Claude Haiku 5.5 refusal carries no fallback credit, so a retry after one pays the full cost of writing the fallback model’s prompt cache.
530532 
531The retry model must be one of the refused model’s permitted fallback targets. For Claude Fable 5.1, Claude Fable 5, and Claude Opus 5.5, those are Claude Opus 4.8 (`claude-opus-4-8`) and Claude Opus 5 (`claude-opus-5`). For Claude Opus 5, it is Claude Opus 4.8. For Claude Sonnet 5.5, it is Claude Sonnet 5 (`claude-sonnet-5`).
533The retry model must be one of the refused model’s permitted fallback targets. For Claude Fable 5.2, Claude Fable 5.1, Claude Fable 5, and Claude Opus 5.5, those are Claude Opus 4.8 (`claude-opus-4-8`) and Claude Opus 5 (`claude-opus-5`). For Claude Opus 5, it is Claude Opus 4.8. For Claude Sonnet 5.5, it is Claude Sonnet 5 (`claude-sonnet-5`).
532534 
533535<Accordion title="Looking up permitted fallback targets programmatically">
534536 On the Claude API and Claude Platform on AWS, the target list is published as `allowed_fallback_models` on each model’s entry in the [Models API](https://platform.claude.com/docs/en/api/beta/models/list) when the `server-side-fallback-2026-07-01` beta header is set. The list is not yet visible under the `fallback-credit-*` header alone. It is not exposed on Amazon Bedrock, Claude Models on Google Cloud (Google managed), or Microsoft Foundry.
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586588 * **`fallback-credit-*`:** keep this header on both requests. The retry needs it to redeem the token.
587589 
588590 <Note>
589 On models that include the 1M token context window by default, such as Claude Fable 5.1, Claude Fable 5, Claude Opus 5.5, Claude Opus 5, Claude Opus 4.8, Claude Sonnet 5.5, and Claude Sonnet 5, the `context-1m-2025-08-07` beta header has no effect. To keep the two requests identical, omit that header on both rather than sending it on one and not the other.
591 On models that include the 1M token context window by default, such as Claude Fable 5.2, Claude Fable 5.1, Claude Fable 5, Claude Opus 5.5, Claude Opus 5, Claude Opus 4.8, Claude Sonnet 5.5, and Claude Sonnet 5, the `context-1m-2025-08-07` beta header has no effect. To keep the two requests identical, omit that header on both rather than sending it on one and not the other.
590592 </Note>
591593</Accordion>
592594 
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653655* Availability: Available
654656* Usage: Needed only when you write the retry yourself: send the `fallback-credit-2026-07-01` beta header and put the refusal’s `fallback_credit_token` on the retry.
655657 
656| Status | Cloud platforms | Models |
657| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
658| Beta | Claude API, [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry) | [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview), [Claude Mythos 5.1](https://platform.claude.com/docs/en/models/mythos-5-1/overview), [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/overview), [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview), [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview), [Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) |
659| Beta<sup>1</sup> | [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed) | [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview), [Claude Mythos 5.1](https://platform.claude.com/docs/en/models/mythos-5-1/overview), [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/overview), [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview), [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview), [Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) |
658| Status | Cloud platforms | Models |
659| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
660| Beta | Claude API, [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry) | [Claude Fable 5.2](https://platform.claude.com/docs/en/models/fable-5-2/overview), [Claude Mythos 5.2](https://platform.claude.com/docs/en/models/mythos-5-2/overview), [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview), [Claude Mythos 5.1](https://platform.claude.com/docs/en/models/mythos-5-1/overview), [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/overview), [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview), [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview), [Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) |
661| Beta<sup>1</sup> | [Amazon Bedrock](https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock), [Claude Models on Google Cloud (Google managed)](https://platform.claude.com/docs/en/build-with-claude/claude-models-on-google-cloud/google-managed) | [Claude Fable 5.2](https://platform.claude.com/docs/en/models/fable-5-2/overview), [Claude Mythos 5.2](https://platform.claude.com/docs/en/models/mythos-5-2/overview), [Claude Fable 5.1](https://platform.claude.com/docs/en/models/fable-5-1/overview), [Claude Mythos 5.1](https://platform.claude.com/docs/en/models/mythos-5-1/overview), [Claude Fable 5](https://platform.claude.com/docs/en/models/fable-5/overview), [Claude Opus 5.5](https://platform.claude.com/docs/en/models/opus-5-5/overview), [Claude Opus 5](https://platform.claude.com/docs/en/models/opus-5/overview), [Claude Sonnet 5.5](https://platform.claude.com/docs/en/models/sonnet-5-5/overview) |
660662 
6616631. On Amazon Bedrock and Google Cloud the token is bound to your caller identity (there are no workspaces), and `allowed_fallback_models` is not exposed.
662664 
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