# Claude Mythos 5.1

Anthropic, released 2026-09-01

**Verdict: conditional.** Same weights as Claude Fable 5.1 at the same $10/$50 rate, with cyber and life-sciences safeguards loosened for vetted users. The catch is access: Mythos 5.1 ships only through Anthropic's trusted-access programs (Cyber Verification and Life Sciences Verification), so there is no self-serve API and no way to buy your way in. Conditional for the same reason as Mythos 5: elite capability behind a vetting gate. Everyone else should use Fable 5.1. Last verified 2026-09-07.

## Pricing

- Input: $10 / 1M tokens
- Output: $50 / 1M tokens
- Context: 1M context, $0.25/1M cache; vetted access

## Strengths

- Vulnerability discovery and offensive-security research — cyber safeguards are loosened relative to Fable 5.1
- Agentic terminal work at the frontier: 60.9% Terminal-Bench 4.0, 5.1 points above Fable 5.1
- Life-sciences work that trips Fable 5.1's biology classifiers, for organizations inside the Life Sciences Verification Program
- Any team not admitted to a verification program — there is no public API and no self-serve path
- General coding and knowledge work — identical price, identical weights, and Fable 5.1 is the one you can actually call
- Organizations outside the US — Anthropic says access is currently limited to a set of US organizations, with international expansion coordinated with the US government but undated

## Benchmarks

- Terminal-Bench 4.0: 60.9% (https://www.anthropic.com/claude-fable-and-mythos-5-1)

## Sources

- [Anthropic — Claude models overview](https://platform.claude.com/docs/en/models/overview)
- [AiCybr — Fable 5.1 / Mythos 5.1 pricing, benchmarks, access](https://aicybr.com/blog/claude-fable-5-1-mythos-5-1-pricing-benchmarks)
- [Anthropic: Claude Fable 5.1 and Claude Mythos 5.1](https://www.anthropic.com/claude-fable-and-mythos-5-1)

Canonical: https://neomanex.com/models/claude-mythos-5-1