Claude found a weakness in a post-quantum signature scheme that two years of expert review had missed

In a 28 July 2026 research post, Anthropic said its Claude Mythos Preview model found a previously unknown mathematical symmetry in the lattice structure of HAWK — a digital signature scheme still under review as a candidate in the US National Institute of Standards and Technology's post-quantum standardisation process — cutting the expected cost of breaking HAWK-256 from 2^64 operations to 2^38. The work took roughly 60 hours with one researcher collaborating, at about $100,000 in model API costs. Nothing in production is affected: HAWK is not a standard yet, and 2^38 operations, while a large reduction, remains far beyond what anyone can practically carry out today. Anthropic disclosed the finding privately to HAWK's own authors in June 2026 and timed public release to the NIST post-quantum mailing list, so the people who review the standard had advance notice rather than a cold announcement.

What it means Anthropic ran this research and is so far the only party to have reproduced it, so the numbers are its own finding until an outside lab checks the maths — but the background assumption should still move: AI-assisted cryptanalysis is demonstrated rather than hypothetical, which makes knowing your own cryptographic inventory the practical next step.