In short
How they differ.
Worked out from the figures below. Prices and specs are the makers' own, read Oct 20, 2026.
- No independent board we follow ranks both models yet.
Side by side
The specs.
| Claude Fable 5.1 | Claude Mythos 5.1 | |
|---|---|---|
| Made by | Anthropic · US | Anthropic · US |
| Released | Sep 1, 2026 | Sep 1, 2026 |
| Price per 1M tokens | $10 in / $50 out | No public price |
| Context window | 1M | Not stated |
| Takes in | text, image | Not stated |
| Download and run it yourself | No | No |
| Size | Not published | Not published |
| Maker says | “For demanding reasoning and long-horizon agentic work” | “Our most capable model for cybersecurity and biology research.” |
| Sources | Prices, Oct 20, 2026 · Description | Prices, Oct 20, 2026 · Description |
Independent tests
Where they place.
Position on each board we follow (1 is best). Epoch AI's and Vectara's scores are shown; the other boards are linked for their own figures.
| Board | Claude Fable 5.1 | Claude Mythos 5.1 |
|---|---|---|
| Epoch Capabilities IndexEpoch AI, Oct 20, 2026 | #4164.65 | Not listed |
| LMArena textLMArena, Oct 15, 2026 | #6 | Not listed |
| LMArena creative writingLMArena, Oct 15, 2026 | #9 | Not listed |
| LMArena coding chatsLMArena, Oct 15, 2026 | #14 | Not listed |
| LMArena WebDevLMArena, Oct 19, 2026 | #5 | Not listed |
| LMArena mathLMArena, Oct 15, 2026 | #2 | Not listed |
| LMArena visionLMArena, Oct 19, 2026 | #17 | Not listed |
| LMArena documentsLMArena, Sep 13, 2026 | #2 | Not listed |
| LMArena Agent ArenaLMArena, Oct 19, 2026 | #3 | Not listed |
| Humanity's Last ExamScale AI | #4 | Not listed |
| SWE-Bench ProScale AI, Sep 22, 2026 | #3 | Not listed |
| Remote Labor IndexScale AI | #3 | Not listed |
| Terminal-Bench 4.0Vals AI, Oct 19, 2026 | #4 | Not listed |
| Vibe Code BenchVals AI, Oct 18, 2026 | #6 | Not listed |
| ProofBenchVals AI, Oct 12, 2026 | #3 | Not listed |
| GPQA Diamond (run by Vals AI, archived)Vals AI, Sep 1, 2026 | #9 | Not listed |
| MMMU Pro (run by Vals AI, archived)Vals AI, Sep 1, 2026 | #1 | Not listed |
| CUA-bench (games)Vals AI, Oct 13, 2026 | #3 | Not listed |
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