On June 9, 2026, Anthropic announced the simultaneous launch of two models. Claude Fable 5 is a "Mythos-class" model made safe for general use: its capabilities exceed those of any model Anthropic has publicly released, reaching state-of-the-art performance on nearly all benchmarks tested. Claude Mythos 5 is the same underlying model, but with guardrails lifted in certain domains; it is restricted to a small group of cyberdefenders and infrastructure providers, deployed initially through Project Glasswing (in collaboration with the US government) as an upgrade to Claude Mythos Preview. Mythos 5 has the strongest cybersecurity capabilities of any model in the world.
Both models are priced at $10 per million input tokens and $50 per million output tokens, less than half the price of Mythos Preview. To deploy quickly and safely, Fable 5 ships with deliberately conservative guardrails (classifiers): on certain topics, the query receives Opus 4.8's response instead. On average, they trigger in fewer than 5% of sessions.
On capabilities, software engineering: Stripe reports that Fable 5 "compressed months of engineering into days," completing a 50-million-line Ruby codebase migration in one day (versus two months for a team). The model achieves the highest score among frontier models on FrontierCode (Cognition). Knowledge work: highest score of any model on Hebbia's Finance Benchmark (senior-level reasoning). Vision: state of the art; reconstructs a web app's source code from screenshots, completes Pokémon FireRed using vision alone. Memory: persistent file-based memory improves its performance 3× more than for Opus 4.8.
Life sciences: with Mythos 5, Anthropic's protein design experts accelerated the process roughly 10×; 9 of 14 protein targets produced strong candidates. Mythos 5 is the first model to generate novel, compelling scientific hypotheses, preferred ~80% of the time in blind comparison; it also conducted autonomous genomics research, training a model 100× smaller that outperforms a recent publication in Science. Automated alignment evaluation places Mythos 5's misaligned behavior at a low level, similar to Opus 4.8. Customer testimonials (Cursor, GitHub, Vercel, EvolutionaryScale) confirm autonomy on long-horizon tasks and reasoning superior to Opus 4.8.