An Anthropic engineer, Steve Weis, announced that he had factored RSA-896 with the help of Claude, Anthropic’s AI model, with the run finishing on September 19, 2026. RSA-896 has 896 bits, or 270 decimal digits, and Weis says its two primes are each 448 bits (about 135 digits) long; multiplying the published factors gives RSA-896. The method was not new: factoring numbers this size uses the General Number Field Sieve, implemented in the open-source CADO-NFS, which set earlier records. What Weis says is new is how the work was carried out: Claude ported CADO-NFS to run on GPUs and orchestrated a fleet of them using scavenged idle capacity. According to Weis, the run used up to 2,048 GPUs at once, over about 10 days, for roughly 30 GPU-years of total computing. The significance is in the process, not the cryptography, as adapting complex software to GPUs and managing thousands of chips across unused capacity normally takes a specialist team a long time. Weis was clear about the limits: there is no new math, Claude did not discover a shortcut, and there is no new factoring algorithm.