Claude Mythos 5

Claude Mythos 5 is Anthropic's most capable model dedicated to cybersecurity and biology research, released on June 9, 2026. It succeeded Mythos Preview (April 2026), bringing noticeable gains on cybersecurity, biology and healthcare benchmarks. Because of the dual-use risk, access is limited to a small set of vetted partners through trusted access programs.

Mythos 5 shares the same underlying model with Claude Fable 5 — Fable is its public variant with robust safeguards: queries touching high-risk domains (cybersecurity, dual-use biology) are automatically routed to Claude Opus 4.8. Mythos 5 does not apply these filters and exposes full capability in these areas.

Under Project Glasswing, the initiative to secure the world's most critical software (partners: AWS, Anthropic, Apple, Broadcom, Cisco, CrowdStrike, Google, JPMorganChase, Linux Foundation, Microsoft, NVIDIA, Palo Alto Networks), the earlier Mythos Preview and about 50 partners found more than 10,000 high/critical severity vulnerabilities across systemically important software. A notable individual example: Mozilla found and patched 271 Firefox vulnerabilities using Mythos Preview within two weeks of limited release.

The availability timeline reflects the weight of these capabilities: on June 12, 2026 the US Department of Commerce suspended access to Mythos-class models under a directive concerning foreign nationals (including Anthropic employees). On June 26, 2026 restrictions were lifted for Mythos 5 for over 100 US organizations. On July 1, 2026 the Trump administration lifted the ban entirely.

Pricing: 10 USD per million input tokens and 50 USD per million output tokens. Use requires accepting a 30-day data retention policy for safety monitoring. Anthropic runs extensive safety evaluations — the full system card describes safety test results. Mythos 5's capabilities in cybersecurity and biology are advanced enough that they could be used for both beneficial and harmful purposes, which justifies the trusted-access model.