Anthropic released fable 5 as the general-access variant of its Mythos-class models, making advanced capabilities available through the Claude API and subscription plans for a staged rollout, the company said.
The company said Fable 5 excels at software engineering, long-context work, vision tasks and scientific research, and that it outperforms earlier Claude models across many benchmarks, including coding and analytical evaluations.
Anthropic said Fable 5 will be included on Pro, Max, Team and seat-based Enterprise plans at no extra cost through June 22, then require usage credits after June 23, with a goal of restoring it to standard subscription features when capacity allows.
Anthropic published pricing for both Fable 5 and Claude Mythos 5 at ten dollars per million input tokens and fifty dollars per million output tokens, and the company described Mythos 5 as the same underlying model with some safeguards lifted for trusted partners.
Safety Measures, Access And Early User Feedback
Anthropic said it deployed new classifiers that detect potential misuse and that when these classifiers flag requests about cybersecurity, biology and chemistry, or distillation, the query is routed to Claude Opus 4.8 rather than being answered by Fable 5.
The company reported that more than 95 percent of Fable sessions run entirely on Fable 5 and that the classifiers trigger in fewer than 5 percent of sessions on average, while acknowledging some benign requests may be caught by the safeguards.
Anthropic described extensive red teaming, saying an internal bug bounty yielded no universal jailbreaks after more than 1,000 hours of testing and that external red-team organizations likewise failed to find universal jailbreaks in long-form agentic tests.
The company said it will require 30-day retention of traffic for Mythos-class models, including Fable 5 and Mythos 5, and that the retained data will not be used to train models and will be used only to defend against novel attacks and reduce false positives.
Anthropic noted a trusted access program for Mythos 5, initially expanding access for cyberdefenders through Project Glasswing in consultation with the US government, and planning a separate trusted program for biomedical researchers with biology safeguards lifted.
Early testers and partners reported strong gains. Stripe said Fable 5 completed a codebase migration in a 50-million-line Ruby codebase in a day that would otherwise take months, and other users praised the model for one-shot app and game creation work.
Independent testers and vendors gave mixed technical feedback: analytics company Hex reported Fable was first to hit 90 percent on a complex analytics benchmark, Jamie Marsland of Automattic highlighted one-shot WordPress theme generation, and researcher Ethan Mollick demonstrated rapid game and mapping prototypes.
