# Anthropic says Claude completed first Lean Fermat's Last Theorem proof > The company said Claude wrote more than 13 million lines of Lean over 11 days and proved tens of thousands of supporting theorems. Anthropic posted the machine-checked sources to GitHub. - Publication: Go Big News - By Go Big News Staff (Staff News) - Category: AI - Published: 2026-09-05T12:04:27.357+00:00 - Canonical: https://www.gobignews.com/ai/anthropic-says-claude-completed-first-lean-fermats-last-theorem-proof --- [Anthropic](https://anthropic.com) said on Sept. 4 that Claude completed the first complete computer-checked proof of Fermat's Last Theorem last month, writing more than 13 million lines in the Lean proof assistant. The company described the work in a post on X and a [Sept. 4 Science Blog post](https://www.anthropic.com/research/formalizing-fermats-last-theorem), and posted the Lean sources to a public [GitHub repository](https://raw.githubusercontent.com/anthropics/fermats-last-theorem/main/README.md). Anthropic said a full formalization had been expected to take years. Sir Andrew Wiles first proved the theorem in 1995, more than 350 years after it was conjectured. The theorem says that no positive integers a, b and c satisfy `a^n + b^n = c^n` for any n greater than 2. Anthropic called Claude's result the largest Lean proof ever written. According to the blog, Claude worked largely on its own for 11 days. Dozens of agents defined concepts, proved intermediate results and assembled them on Prove2Me, an open collaborative formalization platform designed by Anthropic researcher Tianyi Peng and collaborators at Columbia University. The company said human mathematical input was limited to occasional high-level instructions from Peng. The run used about 6 billion output tokens from an internal research model Anthropic described as roughly comparable to [Claude Fable 5.1](https://www.gobignews.com/ai/anthropic-launches-claude-fable-5-1-with-75-cache-read-price-cut). The finished proof is more than five times the size of Mathlib, Lean's principal community library of mathematical proofs, the company said. The GitHub repository lists 29,511 theorems and 1,450 definition modules. Anthropic said Claude produced computer-verifiable proofs of 30,300 theorems during the effort and used 29,500 in the final proof. The argument follows a simplified version of Wiles's proof from Darmon, Diamond and Taylor. Anthropic said Lean checked the proof using only its three standard axioms, while a comparator confirmed the statement matches Mathlib's version of the theorem. The repository says all 60,475 modules built on Lean 4.33.1. It uses Mathlib v4.33.0. Nanoda 0.4.13, an independent Lean kernel written in Rust, also accepted an export of the environment after checking 1,052,234 declarations with no errors. The code is released under the Apache License 2.0 and credits material from Imperial College London's FLT project led by Kevin Buzzard, flt-regular and Mathlib. Buzzard reviewed the proof and said it relies on no assumptions beyond the axioms of mathematics. He also said AI autoformalization work can now serve as a foundation for further proofs. Anthropic said AI-assisted verification could reduce the burden of refereeing mathematics as more proofs are produced, including AI-generated ones. --- ## Companies in this story - Anthropic: https://www.gobignews.com/company/anthropic --- ## X profiles in this story - @anthropicai: https://www.gobignews.com/profile/anthropicai