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Sweep 02 Oct 2026 · 18:55Z Build v2.1.288 509 read Stable v2.1.285 Latest v2.1.288 Next v2.1.288 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Or, for the Project Glasswing model with the same capabilities: changedmodels/fable-5-1/migration-guide

Nearest release: v2.1.287, published 4 hours 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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155815584. **Text between tool calls is returned in thinking blocks:** On Claude Opus 5, text the model writes between tool calls comes back as `text` blocks. On `claude-fable-5-1`, as on Claude Fable 5, that narration comes back as progress-update `thinking` blocks, one before each tool call. Under the default `thinking.display` of `"omitted"`, they carry no readable text. If your interface renders that narration, set `display: "updates"` (beta) to receive progress updates as text while reasoning stays hidden, or `"summarized"` to receive both. Then render the non-empty `thinking` blocks between `tool_use` blocks. See [Progress updates between tool calls](https://platform.claude.com/docs/en/build-with-claude/thinking#progress-updates).
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15605. **Safety classifiers and fallback routing:** Claude Fable 5.1 runs safety classifiers covering the same `stop_details` categories as Claude Fable 5, a broader set than Claude Opus 5's cybersecurity-only classifiers. Expect `stop_details.category` values beyond `"cyber"`, such as `"bio"` and `"reasoning_extraction"`; see the [refusal category table](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response) for the full set. For `fallbacks` configuration and permitted targets, see [Use `fallbacks: "default"` for refusals](https://platform.claude.com/docs/en/models/fable-5-1/migration-guide#fable-5-1-recommended-changes).
15605. **Safety classifiers and fallback routing:** Claude Fable 5.1 runs safety classifiers covering the same `stop_details` categories as Claude Fable 5, a broader set than Claude Opus 5's classifiers. Expect additional `stop_details.category` values, such as `"bio"`; see the [refusal category table](https://platform.claude.com/docs/en/build-with-claude/refusals-and-fallback#refusal-response) for the full set. For `fallbacks` configuration and permitted targets, see [Use `fallbacks: "default"` for refusals](https://platform.claude.com/docs/en/models/fable-5-1/migration-guide#fable-5-1-recommended-changes).
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156215626. **Pricing:** $10 USD per million input tokens and $50 USD per million output tokens, compared with $5 USD and $25 USD for Claude Opus 5. Prompt cache reads are $0.25 USD per million tokens, half the Claude Opus 5 rate. See [Claude pricing](https://platform.claude.com/docs/en/about-claude/pricing).
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