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Claude Fable

closed / Overall score: 4.7(leading)

Claude Fable is Anthropic's Mythos-class tier, built for demanding reasoning, long-horizon agentic coding, knowledge work, vision and scientific research. Fable 5, made generally available in June 2026, is the same underlying model as Claude Mythos 5, wrapped in safeguards that route sensitive cybersecurity, biology, chemistry and distillation requests to a less capable Claude model, with a one-million-token context window and up to 128K output tokens. Fable 5.1 is the current release.

Designated a Covered Model, which carries 30-day mandatory data retention.

Openness

1 high confidence

1.0

weights: closed
data: closed
code: closed
license: Proprietary(API-only)

Anthropic releases no weights, data or code for this model. It is served only through the Anthropic API, closed on every dimension.

https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5 recorded 2026-09-29
The page says "Claude Fable 5 and Claude Mythos 5 carry 30-day data retention" and lists only an API model ID, "claude-fable-5". Searched the body for weights, download, open source, license and self-host: none.

Adoption

4 low confidence

4.0

Claude Fable 5 launched in June 2026 with day-one enterprise testimonials from Cursor, GitHub and Cognition, and was redeployed on July 1, 2026 to the Claude Platform, Claude.ai, Claude Code and Claude Cowork after a pause in access. Anthropic publishes no usage figure, so sustained reach is unproven.

https://www.anthropic.com/news/claude-fable-5-mythos-5 recorded 2026-09-29
Launch post: "Claude Fable 5 is available everywhere today" with early-access testimonials from Cursor, GitHub and Cognition. Searched the body for a user count, weekly users or usage figure: none.
https://www.anthropic.com/news/redeploying-fable-5 recorded 2026-09-29
Redeployment post: "Fable 5 will be available starting tomorrow, Wednesday, July 1, to users globally on the Claude Platform, Claude.ai, Claude Code, and Claude Cowork". Searched the body for a user count, weekly users or usage figure: none.

Capability

5 high confidence

5.0

This score reads Claude Fable 5.1, the tier's current release, which Anthropic recommends for demanding reasoning and long-horizon agentic work. On the Artificial Analysis index it sits in the leading group a few points behind Opus 5.5 and ahead of every model tracked from outside Anthropic, which places it level with Claude Opus.

https://artificialanalysis.ai/leaderboards/models recorded 2026-10-08
The leaderboard's embedded model records, ranked by intelligenceIndex, put Claude Opus 5.5 (Max) first at 57.62, then Claude Sonnet 5.5 (Max) 56.0, Claude Fable 5.1 (Max) 53.35, GPT-6 Astra (Max) 52.67, Gemini 4 Argon (High) 52.56, GPT-6.1 Sol (Max) 51.83 and Muse Spark 1.3 (Max) 48.09 among models not marked deprecated; Grok 4.7 (Xhigh) follows at 46.45, Gemini 3.8 Flash (High) at 40.93, K2 Horizon 375B A23B at 30.5 and Gemini 3.1 Pro Preview at 29.72. The digest drifts between fetches because the page carries live pricing and throughput figures.
https://artificialanalysis.ai/models/claude-fable-5-1 recorded 2026-10-08
Claude Fable 5.1 (Max) "scores 53 on the Artificial Analysis Intelligence Index, placing it well above average among comparable models (median: 26)"; Intelligence rank "# 5 / 225".
https://platform.claude.com/docs/en/models/overview recorded 2026-10-08
Models overview lists "Claude Fable 5.1 Claude Opus 5.5 Claude Sonnet 5.5 Claude Haiku 5.5" as current, and says "start with Claude Opus 5.5 for most workloads. Use Claude Fable 5.1 for demanding reasoning and long-horizon agentic work".

Verified 2026-09-29