Anthropic launched Claude Fable 5, a new Mythos class AI model that the company says is its most capable system made generally available, while keeping a less restricted version limited to trusted cybersecurity partners.
The company said Fable 5 outperforms its previous models across software engineering, knowledge work, vision, scientific research, and other complex tasks. Anthropic said the model’s advantage grows on longer and more demanding assignments, positioning it as a major upgrade over earlier Claude systems.
The release comes with new safeguards because of the model’s stronger capabilities in areas such as cybersecurity and life sciences. When Fable 5 detects certain requests related to cybersecurity, biology, chemistry, or model distillation, the response is routed to Claude Opus 4.8 instead of being handled by Fable 5 directly.
Anthropic said the safeguards were tuned conservatively to allow the model to launch safely and quickly. The company said the fallback system may catch some harmless requests, though it expects the safeguards to trigger in less than 5% of sessions on average.
Alongside Fable 5, Anthropic also launched Claude Mythos 5, which uses the same underlying model but removes some safeguards for a small group of cyberdefenders and infrastructure providers. Mythos 5 will initially be deployed through Project Glasswing in collaboration with the US government as an upgrade to Claude Mythos Preview.
