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The AI models we measure with

Claude Fable 5

Anthropic

Anthropic's most capable model - the sharpest read of how the AI frontier describes your company. A Pro-tier model.

Model details

Model ID
claude-fable-5
Context window
1M tokens
Max output
128k tokens
Knowledge cutoff
Jan 2026
Training data cutoff
Jan 2026

Knowledge cutoff vs training data cutoff

Knowledge cutoff and training data cutoff are different dates: the knowledge cutoff is roughly how current a model's world knowledge is, while the training data cutoff is when its training data ends. Both shape what a model knows about you.

What we use this model for

We ask this model directly about your company to see how it describes you and which names it brings up in your space. It is one of several frontier models in our measurement set, so your visibility is read across the assistants people actually use rather than from a single model.

Recent updates for this model

  1. 3 days ago

    Anthropic researcher Levent Alpöge used Claude Fable 5 to produce a one-line formula providing a counterexample to the Jacobian Conjecture, an algebraic problem unsolved since 1939. Anthropic's Claude Code team reported that Fable 5 demonstrates improved editing and generation capabilities through reduced system prompts and optimized prompt engineering. A service incident on 2026-07-21 caused elevated error rates across five Fable 5 components, including Claude API, Claude Console, and Claude Code, though a fix has since been implemented.

    • Anthropic researcher Levent Alpö ge used Claude Fable 5 to produce a counterexample to the Jacobian Conjecture, a problem unsolved since 1939.
    • A service incident on 2026-07-21 caused elevated errors across Claude API, Claude Console, Claude Code, Claude Cowork, and claude.ai.
    • Claude Fable 5 demonstrated improved editing and generation capabilities via reduced system prompts and prompt engineering optimizations.
    • Anthropic implemented a fix to resolve the elevated error rates affecting Fable 5 components.

    Sources: simonwillison.net, superhuman@mail.joinsuperhuman.ai, noreply@statuspage.io

  2. may be out of date

    Anthropic researcher Levent Alpöge used Claude Fable 5 to produce a one-line formula providing a counterexample to the Jacobian Conjecture, an algebraic problem unsolved since 1939. Anthropic's Claude Code team reported that Fable 5 demonstrates improved editing and generation capabilities through reduced system prompts and optimized prompt engineering. A service incident on 2026-07-21 caused elevated error rates across five Fable 5 components, including Claude API, Claude Console, and Claude Code, though a fix has since been implemented.

    • Anthropic researcher Levent Alpö ge used Claude Fable 5 to produce a counterexample to the Jacobian Conjecture, a problem unsolved since 1939.
    • A service incident on 2026-07-21 caused elevated errors across Claude API, Claude Console, Claude Code, Claude Cowork, and claude.ai.
    • Claude Fable 5 demonstrated improved editing and generation capabilities via reduced system prompts and prompt engineering optimizations.
    • Anthropic implemented a fix to resolve the elevated error rates affecting Fable 5 components.

    Sources: simonwillison.net, superhuman@mail.joinsuperhuman.ai, noreply@statuspage.io

  3. may be out of date

    Anthropic has concluded its Fable 5 access rollout by limiting the model to Max and Team Premium tiers at 50% reduced usage caps. Pro and Team Standard subscribers are being transitioned to pay-per-use API pricing, with Anthropic providing a one-time $100 credit to affected lower-tier users.

    • Anthropic reduced Claude Fable 5 subscription access limits by 50% for Max and Team Premium users.
    • Anthropic transitioned Pro and Team Standard subscribers to pay-per-use pricing for Claude Fable 5.
    • Anthropic issued a one-time $100 credit to lower-tier Claude Fable 5 subscribers.
    • Moonshot AI's Kimi K3 release triggered a brief Nasdaq dip amid competitive comparisons to Claude Fable 5.

    Sources: hi@humanintheloop.online, theprohuman@mail.beehiiv.com, theaireport@mail.beehiiv.com, news@daily.therundown.ai

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