Claude Fable 5.1
Claude Fable 5.1 is an API-only (closed weights) language model from Anthropic, released September 1, 2026. The context window is 1M tokens. On the Epoch Capabilities Index it scores 167.0, rank 7 of 256 rated models. API price: $10 input / $50 output per million tokens.
Claude Fable 5.1 and Claude Mythos 5.1 are the same model, but with different levels of safeguards. Fable 5.1 is generally available, while Mythos 5.1 is available only through our trusted access programs; its safeguards are specifically designed to support work in cybersecurity and the life sciences.
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Strengths by category
ModelTape's 0–100 fit on Epoch AI benchmark results.
| Category | Score | Based on |
|---|---|---|
| Reasoning | 39.9 | Chess Puzzles, SimpleBench, Mystery Game Puzzles, Humanity's Last Exam |
| Math | 79.6 | ProofBench, OTIS Mock AIME 2024-2025, FrontierMath-Tiers-1-3-v2-Private, FrontierMath-Tier-4-v2-Private |
| Coding | 84.1 | GSO-Bench, MirrorCode, FrontierSWE |
Benchmark results
| Benchmark (Epoch AI) | Score |
|---|---|
| ProofBench | 100.0% |
| OTIS Mock AIME | 100.0% |
| FrontierMath (Tiers 1–3) | 94.9% |
| MirrorCode | 93.3% |
| GSO-Bench | 88.2% |
| FrontierMath-Tier-4-v2-Private | 87.8% |
| SimpleBench | 83.9% |
| SimpleQA Verified | 70.8% |
| EBR-bench | 57.1% |
| Furniture Assembly | 57.1% |
| FrontierSWE | 56.3% |
| Mystery Game Puzzles | 53.7% |
| Humanity's Last Exam | 46.5% |
| Chess Puzzles | 45.3% |
| Remote Labor Index | 17.9% |
| SpireClimb | 2.0% |
Links
Announcement · Epoch AI benchmarks
Models with a similar score
Gemini 4 Carbon · GPT-6 Astra · Claude Opus 5.5 · GPT-6.1 Sol · GPT-6.1 Terra · Claude Sonnet 5.5 · Gemini 4 Argon · Claude Opus 5
More from Anthropic
Claude Fable 5.2 · Claude Haiku 5.5 · Claude Sonnet 5.5 · Claude Opus 5.5 · Claude Opus 5 · Claude Sonnet 5 · Claude Fable 5 · Claude Mythos 5