Anthropic Releases Claude Fable 5 and Mythos 5
Fable 5 is broadly available with safeguards, while Mythos 5 is restricted to vetted cyber and infrastructure partners.
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Image Credit- Chetan Jha/ MIT Sloan Management Review India
Anthropic has released Claude Fable 5 and Claude Mythos 5, splitting access to the same advanced AI system between a public model with safeguards and a restricted version for selected cybersecurity and infrastructure partners.
Fable 5 is broadly available through the Claude API and carries added restrictions for cybersecurity, biology and chemistry queries that Anthropic says could be misused. Mythos 5, built on the same underlying model, will remain limited to vetted partners through Project Glasswing, a program Anthropic runs with the US government.
Anthropic said Mythos-class models sit above Opus in capability and have reached a level where they could provide meaningful help in vulnerability discovery and offensive cybersecurity if left unrestricted.
“Without safeguards, Fable 5’s capabilities in areas like cybersecurity could be misused to cause serious damage,” Anthropic said in a statement.
To make Fable 5 available more widely, Anthropic said it added safeguards that route some high-risk requests to Claude Opus 4.8. The filters cover cybersecurity, biology, chemistry and attempts to extract or replicate the model’s capabilities.
The company said the restrictions are tuned conservatively and may sometimes block harmless requests. It expects them to trigger in less than 5% of sessions on average.
Mythos 5 will be offered to a small group of cyberdefenders and infrastructure providers, with some safeguards lifted. Anthropic said it has the strongest cybersecurity capabilities of any model in the world and will initially replace Claude Mythos Preview for approved users.
Project Glasswing began in April with about 50 partners, including large technology, cloud, cybersecurity and financial firms. Anthropic said earlier this month it was expanding the programme to about 150 more organizations across more than 15 countries.
The company also plans a trusted-access program for biology researchers, giving selected users access to Fable 5 with biology and chemistry safeguards removed while keeping cyber restrictions in place.
Fable 5 and Mythos 5 are priced at $10 per million input tokens and $50 per million output tokens.
