Anthropic's Claude Mythos Preview model found a weakness in HAWK, a post-quantum signature scheme, in 60 hours, a flaw that two years of human review had failed to spot. The AI broke HAWK-256, a challenge parameter for researchers, not the HAWK-512 and HAWK-1024 versions for real-world use, reducing key recovery cost from 2 to the power of 64 down to 2 to the power of 38 operations. A second result showed an attack 200 to 800 times faster than the best known method against AES-128 reduced to 7 rounds, requiring encrypting around 2 to the power of 105 attacker-chosen messages. Anthropic stated no production system is affected. The technique against AES, dubbed the Möbius bridge, emerged from three days of near-autonomous work at a cost of around $100,000 in compute, followed by several hundred hours of verification by human researchers. Anthropic notified the HAWK authors in June and coordinated its publication with NIST.