Anthropic launches Claude Fable 5 and a cyberdefender-only Mythos 5 model

Anthropic released Claude Fable 5 and Claude Mythos 5 on June 9, 2026, two frontier models available through the Claude API and priced at $10 per million input tokens and $50 per million output tokens — what the company describes as less than half the price of Claude Mythos Preview.

The split is the point. Fable 5 ships with Anthropic's cybersecurity safeguards intact; Claude Mythos 5 is the same Mythos-class model with those safeguards lifted, available only to vetted Project Glasswing cyberdefenders and critical infrastructure providers. A 30-day data retention policy applies to all Mythos-class traffic.

Anthropic leaned on customer and third-party results to make its case. Stripe said Fable 5 completed a codebase-wide migration across a 50-million-line Ruby codebase in a single day, work it estimated would otherwise take a full team more than two months. Cognition's FrontierCode evaluation ranks Fable 5 highest among frontier models, and Hebbia's Finance Benchmark for senior-level reasoning also places it first, according to Anthropic. Trading firm IMC said the model aced its trading-analysis evaluations nearly across the board.

Those figures are vendor- and customer-supplied and have not been independently verified. On safety, Anthropic said Fable 5 carries classifiers that reroute queries on cybersecurity, biology and chemistry, and model distillation to Claude Opus 4.8, triggering in fewer than 5% of sessions. The UK AI Safety Institute made "progress towards" a universal jailbreak in initial testing, the company said, but none was found across more than 1,000 hours of external bug-bounty work.

Anthropic also pointed to scientific uses of Mythos 5: its internal protein-design team said the model accelerated drug design roughly tenfold, with nine of 14 targets yielding strong candidates, and an autonomous genomics run assembled single-cell data for millions of cells across 138 species.

Fable 5 is included at no extra cost on Pro, Max, Team and seat-based Enterprise plans through June 22, 2026, after which usage credits apply.