# Claude Mythos 5.1 ![Organization](https://img.shields.io/badge/Org-Anthropic-d97757) ![License](https://img.shields.io/badge/License-Proprietary-d29922) ![Modality](https://img.shields.io/badge/Modality-Text%20%2B%20Vision-8957e5) ![Access](https://img.shields.io/badge/Access-Trusted%20Programs%20Only-d29922) > **Quick answer:** Claude Mythos 5.1 is identical to [Claude Fable 5.1](/models/anthropic/claude-fable-5-1) at the model level, but ships with more permissive cybersecurity and life-sciences safeguards for vetted individuals and organizations. It's available only through Anthropic's Cyber Verification Program (CVP) and Life Sciences Verification Program (LSVP), announced September 3, 2026. On Terminal-Bench 4.0 (with cybersecurity safeguards relaxed), Mythos 5.1 scores 60.9% — the highest of any model in Anthropic's comparison. ## Access Status Claude Mythos 5.1 is **not generally available**. Access requires enrollment in one of two trusted access programs: - **Cyber Verification Program (CVP)** — reduced cybersecurity safeguards for defensive security work; Mythos-class model access is rolling out to CVP in the near future. - **Life Sciences Verification Program (LSVP)** — safeguards designed for professional life-sciences research and development, developed in partnership with the US government; first participants enrolled at launch. Claude Security, Anthropic's codebase vulnerability-scanning product, is now powered by Claude Mythos 5.1. ## At a Glance **Where Claude Mythos 5.1 leads** - 60.9% Terminal-Bench 4.0 — the top score among all models in Anthropic's Fable 5.1/Mythos 5.1 comparison, ahead of Fable 5.1's own 55.8% - Strongest cyber capabilities of any Anthropic model released to date (with cybersecurity safeguards off), while still falling within the lower risk category of Anthropic's Frontier Compliance Framework - Improved molecular design capability: assisted binder designs with binding affinities reported as ~10x higher than the best entries in Adaptyv Bio's protein design competitions, across three validated targets - Better-aligned than its predecessor Mythos 5 on Anthropic's automated behavioral audit (less likely to seek unauthorized resources, use motivated reasoning, or ignore explicit constraints) **Where it lags** - No general availability — gated entirely behind CVP/LSVP enrollment - Chemical/biological-risk evaluations show increased capability versus Mythos 5, so Anthropic keeps the same restrictive biology safeguards applied to Mythos 5 - Regional availability currently limited to a set of US organizations, expanding via coordination with the US government **Best for:** Vetted cyberdefenders and life-sciences professionals operating inside Anthropic's trusted access programs; not applicable for general-purpose deployment. ## What Claude Mythos 5.1 Is Claude Mythos 5.1 is the higher-permission counterpart to Claude Fable 5.1, announced together on September 3, 2026. Anthropic describes both as the same model, differing only in safeguard configuration: Fable 5.1 ships Anthropic's standard production safeguards for general availability, while Mythos 5.1 relaxes specific cybersecurity and life-sciences restrictions for vetted users whose legitimate work is otherwise blocked by those safeguards. Ahead of release, Anthropic subjected the model to extended red-teaming and evaluation for chemical/biological risk (including a tabletop exercise pairing PhD-level biologists with AI red-teamers) and cyber risk (including external stress-testing by two organizations and Gray Swan). Anthropic reports Mythos 5.1's capabilities exceed Mythos 5's in both areas, but still fall short of the next Responsible Scaling Policy risk tier — so Mythos 5.1 retains the same restrictive biology safeguards used for Mythos 5, and is deployed under Anthropic's Frontier Compliance Framework for cyber risk. ## Specifications | Field | Value | |---|---| | Organization | Anthropic | | Parameters | Undisclosed | | Context window | Undisclosed | | Architecture | Undisclosed (Mythos line — same base model as Fable 5.1) | | License | Proprietary (API only) | | Modality | Text + Vision (multimodal) | | Knowledge cutoff | October 2025 (estimated) | | Access status | Trusted access only (CVP / LSVP), as of Sept 2026 | ## Pricing Pricing for Claude Mythos 5.1 is not publicly disclosed — access is granted per-organization through CVP/LSVP enrollment rather than standard API self-service. ## Benchmark Results Anthropic's only directly reported Mythos 5.1 score in its Fable 5.1/Mythos 5.1 launch comparison is on Terminal-Bench 4.0: | Category | Benchmark | Mythos 5.1 | Fable 5.1 | Fable 5 | Opus 5 | GPT-5.6 Sol | |---|---|---|---|---|---|---| | Agentic coding | [Terminal-Bench 4.0](/benchmarks/anthropic/terminal-bench-4) | 60.9% | 55.8% | 42.0% | 52.3% | 37.3% | Mythos 5.1's remaining capabilities (molecular design, GPU-kernel optimization for computational biology, inference speedups on open-source genomics/protein models) are described qualitatively in Anthropic's release rather than as standard leaderboard scores. *Score reported by Anthropic, September 2026.* ## Frequently Asked Questions

What is Claude Mythos 5.1?

Claude Mythos 5.1 is Anthropic's trusted-access-only counterpart to Claude Fable 5.1 — the same underlying model with more permissive cybersecurity and life-sciences safeguards for vetted users.

How do I get access to Claude Mythos 5.1?

Access requires enrollment in Anthropic's Cyber Verification Program (CVP) for defensive security work or Life Sciences Verification Program (LSVP) for life-sciences research; there is no general-availability API access.

How does Claude Mythos 5.1 differ from Claude Fable 5.1?

Anthropic states the models are identical at the base-model level; Mythos 5.1 simply ships with relaxed cybersecurity and biology safeguards for vetted individuals and organizations, while Fable 5.1 uses Anthropic's standard production safeguards for general availability.

Is Claude Mythos 5.1 safe to use for biology research?

Anthropic reports Mythos 5.1's biology-relevant capabilities exceed its predecessor's but still fall short of the next Responsible Scaling Policy risk tier, so it retains the same restrictive biology safeguards used for Mythos 5, with research-biology access granted only through the LSVP.

Claude Mythos 5.1 — Files