Head to head
Claude Mythos 5.1 vs Claude Fable 5.1
Claude Mythos 5.1 from Anthropic against Claude Fable 5.1 from Anthropic — specification, price and every benchmark both makers have published, in one table.
Benchmarks
Claude Mythos 5.1 leads
Claude Mythos 5.1 wins 1 of the 1 benchmarks both models report, Claude Fable 5.1 wins 0, consistently. The average gap across shared tests is 5.1 points.
Price
Same price
Both cost $20.00 per million tokens on a 3:1 input-to-output mix.
What actually differs
- Claude Mythos 5.1 is not generally available. Access is invitation only — Project Glasswing. Claude Fable 5.1 can be called by anyone with an API key, and on identical specifications that is the difference that decides it.
Scorecard
Which is better at what
Maths, coding, reasoning and the rest — one line each, averaged over the benchmarks both models actually report.
| Category | Claude Mythos 5.1 | Claude Fable 5.1 | Better at this |
|---|---|---|---|
| ReasoningNeither model reports this | — | — | Not comparable |
| MathsNeither model reports this | — | — | Not comparable |
| CodingTerminal-Bench 4.0 | 60.9% | 55.8% | Claude Mythos 5.1+5.1 |
| KnowledgeNeither model reports this | — | — | Not comparable |
| MultimodalNeither model reports this | — | — | Not comparable |
| Instruction followingNeither model reports this | — | — | Not comparable |
| Human preferenceNeither model reports this | — | — | Not comparable |
| Categories wonOut of 1 comparable | 1 | 0 | Claude Mythos 5.1 |
Each category averages only the benchmarks every model here reports, so no one is credited for a test the other did not run. A category with no shared test is marked Not comparable rather than guessed at.
Side by side
Claude Mythos 5.1 and Claude Fable 5.1, row by row
| Attribute | Claude Mythos 5.1Anthropic | Claude Fable 5.1Anthropic |
|---|---|---|
| Specification | ||
| MakerWho built it | Anthropic | Anthropic |
| Released | 2026-09 | 2026-09 |
| Context windowHow much can go in at once | 1,000,000 tokens | 1,000,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Input | Text, Image | Text, Image |
| ReasoningSpends extra tokens thinking before it answers | Yes | Yes |
| Tool calling | Yes | Yes |
| Knowledge cutoff | 2026-06 | 2026-06 |
| Licence | Proprietary | Proprietary |
| AvailabilityWhether anyone can call it, or access is approved case by case | Invitation only — Project Glasswing | Not reported |
| Open weightsCan you download and run it yourself | No | No |
| Price | ||
| Input priceUSD per million tokens in | $10.00 | $10.00 |
| Output priceUSD per million tokens out | $50.00 | $50.00 |
| Cached input | $0.25 | $0.25 |
| Blended 3:1A 3-in-to-1-out million-token mix — a fairer single number than input price alone | $20.00 | $20.00 |
| Published benchmarks | ||
| SWE-bench ProA harder, contamination-resistant successor to SWE-bench Verified, drawn from commercial and copyleft repositories that were never public training data. | Not reported | |
| Terminal-Bench 4.0End-to-end tasks in a real terminal — install, build, debug, run — scored on whether the machine ends up in the required state. | ||
| Links | Full page | Full page |
| Row verified | 2026-09 | 2026-09 |
Where these numbers come from
Every score on this page is a published figure, taken from the model's own card, system card, technical report or release post, or from a public leaderboard. CorX Labs did not run these evaluations. Most are self-reported by the lab that built the model, which means they were produced under that lab's own choice of prompt, scaffold and number of attempts — so treat them as a starting point for a shortlist, not as a settled ranking.
A score someone other than the model's maker measured is marked Independent and names its measurer. Those are the stronger numbers on this page — an outside harness has no reason to flatter anyone — and there are not many of them.
Where a figure has not been published, the cell reads Not reported rather than an estimate. Nothing here is inferred, interpolated or guessed. Each model records the month its row was last checked. Full method and caveats.
Questions
Claude Mythos 5.1 or Claude Fable 5.1?
Is Claude Mythos 5.1 better than Claude Fable 5.1?
Claude Mythos 5.1 wins 1 of the 1 benchmarks both models report, Claude Fable 5.1 wins 0, consistently. The average gap across shared tests is 5.1 points.
Which is cheaper, Claude Mythos 5.1 or Claude Fable 5.1?
Both cost $20.00 per million tokens on a 3:1 input-to-output mix.
What is the difference between Claude Mythos 5.1 and Claude Fable 5.1?
Claude Mythos 5.1 is not generally available. Access is invitation only — Project Glasswing. Claude Fable 5.1 can be called by anyone with an API key, and on identical specifications that is the difference that decides it.
