Data as of October 16, 2026 · How the score is built
Released Sep 1, 20261M contextClaude Fable 5.1 and Claude Mythos 5.1 system card
Claude Mythos 5.1
Decision readingClaude Mythos 5.1 is tracked, but not publicly ranked yet. The profile exposes 1 sourced benchmark rows and leaves unsupported fields blank until a published record exists.
Released Sep 1, 2026 — see all recent releases
Decision snapshot
Each value carries a field reference instead of floating alone. Markers compare this model with the current ranked and priced catalog; they are not absolute quality thresholds.
Capability
Unranked
field median 49.6Not eligible for a public rank
Price
API rate not published
input median $0.75No comparable first-party hosted token rate
Speed
Not measured
field median 92 tok/sTime to first token not measured
Context
1Mtokens
field median 256,000Maximum output length is tracked separately
Strongest published evidence
Published rows are visible, but no category has enough eligible evidence for a comparative rank.
Validate before choosing
1 published rows leave some tracked benchmark slots empty. No comparable first-party API token rate is published.
Source-linked · 1 displayable benchmark row
Category score record
Scores and ranks appear only where published evidence can be displayed. The table keeps the score, weight, cohort, and evidence state together.
| Category | Score | Rank | Percentile | Weight | Benchmarks | Evidence |
|---|---|---|---|---|---|---|
| AgenticWeight 22%1 benchmarkVerified | Score pending | 1 benchmark | Verified | |||
| CodingWeight 20%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured | |||
| ReasoningWeight 17%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured | |||
| MultimodalWeight 12%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured | |||
| KnowledgeWeight 12%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured | |||
| MultilingualWeight 7%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured | |||
| Inst. FollowingWeight 5%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured | |||
| MathWeight 5%0 benchmarksNot measured | Not measured | 0 benchmarks | Not measured |
1 of 681 tracked benchmark slots have displayable evidence · bars run 0–100
Coverage detailsHow much of this is verified
Coverage is split by category so a strong number never hides a thin evidence base. Verified means the row is tied to a published source; provisional rows remain visible but separate.
- Agentic1/1 verified
- CodingNot measured
- ReasoningNot measured
- MultimodalNot measured
- KnowledgeNot measured
- MultilingualNot measured
- Inst. FollowingNot measured
- MathNot measured
Benchmark ledger
Agentic opens by default. The marker compares each value with the best source-verified result in the catalog; provisional leaders do not set the reference. Expand the remaining categories for every published row.
Agentic1 row
| Benchmark | Score | Versus best verified row | Gap | Weight | Evidence |
|---|---|---|---|---|---|
| Terminal-Bench 4.0 | Score60.90% | Versus best verified row Best verified: Claude Sonnet 5.5 · 70.60% | Gap9.7 behind | Weight8% ref. weight |
Bars run 0–100; the dark tick marks the best source-verified value
All 1 rowsLineage
The sequence follows explicit supersedes links. Each score is estimated for that model; a relative can inform a sparse estimate but never sets a floor, so a newer release can score below an earlier one. Scores and prices remain blank when the corresponding public row or first-party rate is unavailable.
Spec sheet
Each documented value carries its source. Missing fields stay visible as not sourced or not published, rather than disappearing from the page.
- API model ID
- Not publishedAnthropic Fable 5.1 and Mythos 5.1 launch
- Context window
- 1MClaude Fable 5.1 and Claude Mythos 5.1 system card
- Maximum output
- Not sourced yet
- Knowledge cutoff
- Not sourced yet
- Input modalities
- Not sourced yetClaude Fable 5.1 and Claude Mythos 5.1 system card
- Output modalities
- Not sourced yetClaude Fable 5.1 and Claude Mythos 5.1 system card
- Parameters
- Not disclosed by the provider
- Availability
- Cyber Verification Program · Life Sciences Verification Program · Claude SecurityAnthropic Fable 5.1 and Mythos 5.1 launch
- Cloud regions
- Not tracked yet
- Lifecycle
- limited accessAnthropic Fable 5.1 and Mythos 5.1 launch
- API capabilities
- Tool calling, structured outputs, and batch support are not tracked yet
- Prompt caching
- Not documented in the pricing recordAnthropic Fable 5.1 and Mythos 5.1 launch
- Self-host
- Weights are not published
- Rate limits
- Not tracked yet
How to read this profile
The visual layer above carries the decisions. These notes preserve the model, ranking, coverage, and family context behind the numbers.
We track Claude Mythos 5.1, but the public leaderboard excludes this profile until enough non-generated benchmark coverage is available. Only published rows appear above.
Claude Mythos 5.1 is a proprietary model with a 1M context window. It uses an explicit reasoning mode, which can improve complex problem solving while adding latency and token use.
Limited to vetted cyberdefenders and life scientists through Anthropic's trusted access programs. Access currently covers selected US organizations while Anthropic coordinates expansion with the US government; Claude Security also uses Mythos 5.1 for vulnerability scanning and human-reviewed patch suggestions.
Anthropic says Claude Mythos 5.1 and Claude Fable 5.1 use the same underlying model with different safeguards. We do not copy Fable results onto the restricted profile. The only stored score is Anthropic's exact Mythos 5.1 Terminal-Bench 4.0 result, where the safeguard configuration materially changes the evaluated system.
Claude Mythos 5.1 sits in the Claude Mythos family with Claude Mythos 5, Claude Mythos Preview. Its explicit predecessor is Claude Mythos 5. 1 of 681 tracked benchmark slots currently have displayable evidence. Missing categories stay blank.
Last updated October 16, 2026. Runtime fields remain blank until a sourced snapshot exists.
Questions
How does Claude Mythos 5.1 perform overall in AI benchmarks?
Claude Mythos 5.1 has 1 source-displayable benchmark rows, but it does not qualify for a public overall rank. The available rows remain visible by category without being converted into a site-wide score. Missing evidence stays blank instead of being estimated from an earlier model.
Is Claude Mythos 5.1 good for agentic tool use and computer tasks?
Claude Mythos 5.1 has source-displayable benchmark coverage for agentic tool use and computer tasks, but the public category table does not assign it a rank there. The individual rows remain available for inspection. A missing category position means the evidence threshold was not met; it does not convert the model's unmeasured work into a zero.
Which sibling models are related to Claude Mythos 5.1?
Claude Mythos 5.1 belongs to the Claude Mythos family. Related tracked variants include Claude Mythos 5, Claude Mythos Preview. A sibling link indicates shared lineage or a documented configuration relationship; it does not mean the variants have identical pricing, context limits, benchmark evidence, or deployment behavior. Compare before switching.
Does Claude Mythos 5.1 have full benchmark coverage on BenchLM?
No. Claude Mythos 5.1 currently has 1 source-displayable rows across 681 tracked benchmark slots. The profile exposes published, non-generated evidence and leaves missing categories blank until an exact evaluation is available. Coverage describes how much was measured; it is not a penalty added to an individual benchmark result.
What is the context window size of Claude Mythos 5.1?
Claude Mythos 5.1 has a documented context window of 1M. That figure is the maximum combined prompt and retained-conversation space reported for this exact model; it is not the maximum output length. The profile keeps output limits separate because providers often publish those limits independently.