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Sweep 03 Nov 2026 · 22:27Z Build v2.1.318 536 read Stable v2.1.311 Latest v2.1.318 Next v2.1.318 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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whats-new-fable-5-1 changedmodels/fable-5-1/whats-new-fable-5-1

Nearest release: v2.1.317, published 7 hours after 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 1 Sep 2026 this site's first read of the page
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8989### Change effort mid-conversation (beta)
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91On Claude Fable 5.1 you can change the [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level mid-conversation without invalidating the prompt cache. Raise it for a hard step and lower it for routine ones. Per-message effort is in beta: include the `mid-conversation-output-config-2026-07-01` beta header. Claude Fable 5.1 and Claude Mythos 5.1 support it on the Claude API, Claude Models on Google Cloud (Google managed), and Amazon Bedrock. To use it with Claude Fable 5.1 through the Amazon Bedrock [InvokeModel API](https://platform.claude.com/docs/en/build-with-claude/claude-on-amazon-bedrock-legacy), send that value in the `anthropic_beta` array of the request body instead. For the other models that support it and the platforms for each, see [Change effort mid-conversation](https://platform.claude.com/docs/en/build-with-claude/effort#changing-effort-mid-conversation).
91On Claude Fable 5.1 you can change the [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level mid-conversation without invalidating the prompt cache. Raise it for a hard step and lower it for routine ones. Per-message effort is in beta: include the `mid-conversation-output-config-2026-07-01` beta header. To use it with Claude Fable 5.1 through the Amazon Bedrock [InvokeModel API](https://platform.claude.com/docs/en/build-with-claude/claude-on-amazon-bedrock-legacy), send that value in the `anthropic_beta` array of the request body instead. For the models and platforms that support it, see [Change effort mid-conversation](https://platform.claude.com/docs/en/build-with-claude/effort#changing-effort-mid-conversation).
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