Anthropic launched this Tuesday (9) Claude Fable 5, its most capable artificial intelligence model available to the general public. The new system, from the Mythos class, brings significant advances in coding, reasoning and visual tasks, while maintaining safeguards to limit risks.
Fable 5 especially excels in software engineering. Stripe reported that the model performed a complete migration on a 50 million line Ruby codebase in just one day — a task that would have required an entire team for more than two months.
Benchmark performance
In independent evaluations, Fable 5 achieved the best results among frontier models in Cognition’s FrontierCode, which tests code quality in production. In the cybersecurity ExploitBench, it reached 78%, more than double that recorded by competitors such as GPT-5.5.
In Hebbia’s financial benchmark, aimed at senior-level reasoning, the model led handily, with significant gains in interpretation of documents, graphs and tables. He also reconstructed web application source code from just screenshots.
Fallback security mechanism
To balance capacity and security, Fable 5 includes classifiers that automatically redirect sensitive queries — involving cybersecurity, biology, or chemistry — to Claude Opus 4.8. Anthropic reports that this occurs in less than 5% of sessions, and the user is always notified.
This approach allows you to release high computational power without exposing the model to potentially harmful uses.
Mythos 5 for restricted use
In parallel, the company makes Claude Mythos 5 available to a limited group of partners via Project Glasswing, an initiative in collaboration with the United States government and large technology companies. This version maintains the same basis as Fable 5, but with safeguards removed in specific areas, focusing on cyber defense and critical infrastructure.
Anthropic plans to expand access through a trusted partner program. For now, Mythos 5 remains out of reach of the general public.
Price and availability
Claude Fable 5 is now available. The cost is $10 per million tokens in and $50 per out. On Pro, Max, Team and Enterprise plans, access is included at no additional cost until June 22nd. After this date, you will need to use credits.
The launch comes at a time of strong demand for AI tools that accelerate software development and complex analysis, with Fable 5 positioned as a practical solution for teams tackling large-scale projects.
