Anthropic engineer factors RSA‑896 with Claude and 2,048 idle GPUs

Steve Weis, an engineer at Anthropic, published a 135-digit factor of RSA-896 on Saturday, a 270-digit challenge number from the RSA Factoring Challenge list of 1991. His write-up says Claude ported CADO-NFS, an open-source implementation of the number field sieve, to GPUs, and that the run used about 30 GPU-years over ten days on up to 2,048 GPUs.

Weis was explicit about what it does not mean. There were no algorithmic improvements, factoring remains subexponential in the key size, and there is no new threat to deployed keys, he wrote. Deployed RSA-2048 keys are about a billion times harder than RSA-1024, which is itself roughly 30 times harder than RSA-896, according to one cryptography commentator.

The compute was scavenged. Weis said the job ran at the lowest priority on GPUs Anthropic already owned, in gaps between real work, and that the main engineering difficulty was constant pre-emption and recovery. He said he did not intervene: the model fixed discovered bugs such as out-of-memory errors on its own.

It is the third record in sixteen days. Andrew Curran noted that the public factoring record moved from 829 bits to 862 and now 896, each with AI assistance. Cognition's Devin agents took RSA-260 earlier this month. Weis said he had been working on RSA-260 when Cognition beat him to it, using the same approach. One reader verified that the published factor multiplies out to the full modulus.