Anthropic Completes Training of New Mythos; Sonnet 5 Expected This Week

Anthropic has positioned Claude Mythos 5 as its most powerful cybersecurity model, making its capabilities and access controls consequential for critical infrastructure protection and AI governance. With the public-facing Fable 5 still blocked, the gap between government and civilian access to advanced models has fueled controversy over technological monopolies and double standards.

Anthropic recently announced that Mythos 5 had been cleared to come back online, but only for certain US critical infrastructure organizations, with no access for the general public. Fable 5 remains blocked. Anthropic did not disclose the exact announcement date, the number of authorized organizations or any financial amounts involved, prompting criticism from the online and open-source communities that it is using AI risks to entrench national and technological advantages.

Anthropic has long competed in the generative AI market with its Claude model family, while its Mythos-class models were previously available only to governments and selected organizations. Claude Fable 5 brings capabilities in the same class to the public for the first time, marking a shift in advanced AI from closed deployments toward commercial use. The move is also drawing greater attention to software development, cybersecurity and biological-risk governance.

Anthropic unveiled Claude Fable 5 and Mythos 5 on June 10, claiming a performance improvement of more than 10% over the previous generation. Fable 5 is priced at twice the cost of Opus 4.8 and includes three layers of safety protections and model-distillation detection, while sensitive queries can be routed to other models. Mythos 5 remains restricted to governments and authorized organizations.