Anthropic's restricted frontier AI model, Claude Mythos Preview, found a meaningful structural flaw in HAWK, a leading candidate for post-quantum digital security standards, in 60 hours after two years of expert human cryptanalysis failed, effectively cutting its key strength in half. Anthropic's cryptanalysis research blog published the full findings on July 28, 2026. The same model, working mostly on its own over three days, invented a new attack technique named the Möbius Bridge that makes an existing attack on a weakened version of AES between 200 and 800 times faster, as detailed in Anthropic's AES Möbius Bridge paper. Neither finding breaks anything protecting real-world data right now, as HAWK has not been deployed anywhere and the AES result targets a deliberately weakened research variant. HAWK is a digital signature scheme designed for a world where quantum computers exist at scale, and it is the only lattice-based scheme among the nine candidates NIST advanced to the third round of its additional post-quantum digital-signature process in May 2026.