Stay cool: Mythos 5 is an upgrade over Mythos Preview while Fable 5 is Mythos "made safe for general use," Anthropic explained.
June 12, 2026
The launch of Anthropic's Claude Fable 5 and Mythos 5 models put frontier capabilities into more hands, but experts say the security story more or less remains the same: Don't panic, do prepare.
Anthropic this week released the latest versions of its Claude models, Mythos 5 and Fable 5. Claude Mythos 5 is the next iteration of Claude Mythos Preview, a frontier model offered to a small number of organizational partners in April. Anthropic claims that Mythos is so capable of finding and exploiting vulnerabilities that the company said Mythos could find critical exploits in popular, decades-old software.
Because of this supposed danger, the company launched a secondary campaign, Project Glasswing, in order to give cybersecurity partners a headstart and limit the potential for Mythos to be misused by threat actors. Even under Glasswing, access was restricted and monitored.
