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TRACKING · Tracking record

Claude Fable 5.1 · Records and changes

The Anthropic Claude version currently represented in the workbench.

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UNDERSTANDING · What we know

Uses, conditions and important changes.

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Claude Fable 5.1 · Reading revised · 5 Sept 2026

Claude Fable 5.1 tops the AA index; cache reads cut to 2.5% of input

Anthropic shipped Claude Fable 5.1, successor to Fable 5 for long-running agentic coding, knowledge work, and research, alongside Mythos 5.1 for Project Glasswing participants. Defaults: 1M-token context, 128k max output, always-on adaptive thinking at $10/$50 per MTok with prompt-cache reads cut to $0.25/MTok (0.025x base input versus 0.1x elsewhere). Live on Claude API, Bedrock, AWS, Google Cloud, Microsoft Foundry, and OpenRouter at matching prices. Artificial Analysis now ranks it #1 of 192 (index 66 vs 62 for Fable 5); cost per index task is $3.69 vs $3.14, about 18% higher.

Evidence is Anthropic's official release notes (vendor's own account) plus the Artificial Analysis leaderboard (third-party measurement, fetched and checked by BitShovel on Sep 2, 2026), cross-reported the same day by aihot and AlphaSignal. The ~18% per-task delta is computed from AA's $3.69 vs $3.14, slightly under the 20% rounding in aggregator headlines. An index rank is not a substitute for independent evaluation, and leaderboard attention is not proof of fit.

Read the record and sources →

Changes and reading revisions

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THE FULL RECORD · Full timeline

3 events retained by the site.

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Claude Fable 5.1Events retained by the site
  1. On radarClaude Fable 5.1 tops the AA index; cache reads cut to 2.5% of input
  2. On radarEntered the BitShovel radar: 50 entries visible on AIHOT featured at collection.
  3. CorroborationCorroboration added: Simon Willison's weblog carried the same story this window (title match).

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COVERAGE · Record status

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Registered follow-up scope

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  • Claude Fable 5.1

    Official revisions to Fable-series pricing, capabilities, or API behavior, plus any public widening of Mythos 5.1

    Open the tracked source ↗

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THE LINEAGE · Lineage

Explore earlier and later versions.

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