Claude Just Produced the First Computer-Checked Proof of Fermat's Last Theorem

Sun, 06 Sep 2026 09:00:00 +0530

On September 4, Anthropic disclosed that Claude, working largely autonomously over 11 days, produced the first end-to-end, computer-checked proof of Fermat’s Last Theorem in the Lean proof assistant. Along the way it wrote 13 million lines of Lean code and proved 29,500 intermediate theorems, more than five times the size of Mathlib, the community library those theorems build on.

This matters less because of the theorem itself, Andrew Wiles already proved Fermat’s Last Theorem in 1995, and more because of what got checked. Wiles’s proof ran 129 pages and took a team of expert reviewers over a year to verify; two months into that process, a reviewer’s question exposed a gap that took Wiles another year to close. Formalizing a proof in Lean removes that ambiguity entirely: either the proof assistant accepts every step down to Lean’s three basic axioms, or it does not. What used to take human referees years now took a fleet of agents eleven days, and that compression is the actual story for anyone tracking what AI does to the economics of verification.

Mathematics on Kuldeep Pisda

Claude Just Produced the First Computer-Checked Proof of Fermat's Last Theorem