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Fable 5 is state-of-the-art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. The longer and more complex the task, the larger Fable 5’s lead over our other models.
Releasing a model this capable comes with risks. Without safeguards, Fable 5’s capabilities in areas like cybersecurity could be misused to cause serious damage. Queries on a narrow range of topics will instead receive a response from our next-most-capable model, Opus 4.8.
Fable 5’s safeguards detect requests related to cybersecurity, biology and chemistry, and distillation. Users are informed whenever a fallback occurs—on average in less than 5% of sessions. We’ll keep refining the safeguards to reduce false positives.
For a small group of cyber defenders and critical infrastructure providers, we are also launching Claude Mythos 5. Mythos 5 shares the same underlying model as Fable 5, but with the safeguards lifted in some areas.
Soon, we intend to expand access to Mythos 5 through a broader trusted access program, both for defensive cybersecurity work and biomedical research.
Claude Fable 5 is available everywhere today. Claude Mythos 5 is restricted to Glasswing partners until we expand our trusted access program.