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    Anthropic Releases Lean Proof of Fermat's Last Theorem

    Anthropic says its model produced the first end-to-end computer-checked version of the theorem.

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    32 Sources, 26d ago, first seen 26d ago

    TLDR

    Anthropic posted that its model Claude turned Andrew Wiles' 1995 proof of Fermat's Last Theorem into a Lean formalization spanning 13 million lines and 29,500 intermediate theorems. The company called it the largest Lean proof constructed and published the code on GitHub. The Lean account and several researchers shared the announcement. Replies on X noted the scale compared to Mathlib and asked about verification limits. Other posts highlighted that the work converts an existing human proof rather than generating a new one.

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    32 Sources, first seen 26d ago

    Combined views

    5M

    32 Sources, first seen 26d ago

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    Sentiment

    Positive71.2%28.8%Negative

    Summary

    Sentiment

    Positive71.2%28.8%Negative

    Many accounts welcomed Anthropic's Lean proof of Fermat's Last Theorem as a breakthrough in automated formalization, while negative replies dismissed its value due to its massive unreadable size and self-reported results.

    Based on 60 sentiment-bearing replies from 52 accounts across 8 conversations.

    Summary

    Many accounts welcomed Anthropic's Lean proof of Fermat's Last Theorem as a breakthrough in automated formalization, while negative replies dismissed its value due to its massive unreadable size and self-reported results.

    Based on 60 sentiment-bearing replies from 52 accounts across 8 conversations.

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    32 Sources

    @AnthropicAIChecking that a major mathematical proof is correct can take years. Formalization—converting the mathematical reasoning into a form computer proof assistants like Lean can verify—can help. Last month, Claude completed the first formalized proof of Fermat’s Last Theorem, one of the most famous theorems of all time. This was a project experts thought would take many years. It is the largest Lean proof ever written. Fermat’s Last Theorem was first proven in 1995 by Sir Andrew Wiles, more than 350 years after it was conjectured. Our proof, which totals over 13 million lines of code, provides machine verification. More importantly, it proves over 29,000 other theorems that the proof requires, across many areas of math which had never before been formalized. We see this as a major step in the long process of firming up the core of mathematical knowledge, building on work from three centuries of mathematicians and hundreds of contributors to Lean and Mathlib. We are optimistic that AI-assisted verification of mathematical proofs will help reduce the burden of refereeing mathematics in an era where more proofs are being produced than ever before. You can read about the process on our Science Blog: https://www.anthropic.com/research/formalizing-fermats-last-theorem And see the complete proof on GitHub: https://github.com/anthropics/fermats-last-theorem
    @sammcallister“This extraordinary autoformalization achievement, which Anthropic researchers say only took 11 days, proves Fermat’s Last Theorem with no assumptions other than the axioms of mathematics. Along the way we see autoformalization of algebra, harmonic analysis, geometry and number theory, and we learn that AI autoformalization artefacts are now robust enough to be built upon; the proof is multi-layered.” https://www.anthropic.com/research/formalizing-fermats-last-theorem
    @Leonard41111588I did not expect this. Anthropic just published a Lean proof of Fermat's Last Theorem. The proof is +13M LoC, more than 5 times the size of Mathlib. Kevin Buzzard's post: https://xenaproject.wordpress.com/2026/09/04/flt-anthropic-has-beaten-me-to-it/ The proof: https://github.com/anthropics/fermats-last-theorem Anthropic's post: https://www.anthropic.com/research/formalizing-fermats-last-theorem
    @leanprover@AnthropicAI has shared the first end-to-end, computer-checked proof of Fermat's Last Theorem: 13 million lines of Lean, 29,500 intermediate theorems. Their announcement calls it "the largest Lean proof ever constructed." See also Kevin Buzzard's blog post about the proof: https://xenaproject.wordpress.com/2026/09/04/flt-anthropic-has-beaten-me-to-it/ 🔗 Anthropic's announce post: https://www.anthropic.com/research/formalizing-fermats-last-theorem 🔗 The code: https://github.com/anthropics/fermats-last-theorem #LeanLang #LeanProver #FLT
    @patrickshaftoRT @Leonard41111588: I did not expect this. Anthropic just published a Lean proof of Fermat's Last Theorem. The proof is +13M LoC, more th…
    @CsabaSzepesvari@AnthropicAI Old question, I will sound like a broken grammaphone: How do we know this formalization is correct? I would like to learn about the efforts made on this and a honest discussion of the limits of these efforts. Please please..
    @ShayneRedfordClaude formalized Fermat's Last Theorem in 11 days! 🚀 This spans 29k intermediate theorems, and 13M lines of Lean. For scale, Mathlib in it's entirety is ~8k files and 2.2M lines. This shows tremendous promise to automatically formalize massive swathes of modern mathematical literature, starting from the elementary vocabulary in Mathlib. Congratulations to @tianyi_peng who led this effort! https://www.anthropic.com/research/formalizing-fermats-last-theorem
    @nickcammarataimagine explaining to fermat that we had a guy in a computer write fourteen million lines of lean but we have a pretty good grasp on his conjecture now
    @allenainieThis is quite credible. I have read some of @tianyi_peng’s Markovian interference work, but this is absolutely mind blowing. It’s also a huge victory for decades of efforts in auto-formalization. AI is uplifted by years of human hard work.
    @patio11If you had told me in undergrad I’d love to see ~fully automatic formalization I would have bet against, and if you had told me that the machine doing it would have a running color commentary on the importance, I’d have thought you under the influence. https://www.anthropic.com/research/formalizing-fermats-last-theorem

    32 Sources

    @AnthropicAIChecking that a major mathematical proof is correct can take years. Formalization—converting the mathematical reasoning into a form computer proof assistants like Lean can verify—can help. Last month, Claude completed the first formalized proof of Fermat’s Last Theorem, one of the most famous theorems of all time. This was a project experts thought would take many years. It is the largest Lean proof ever written. Fermat’s Last Theorem was first proven in 1995 by Sir Andrew Wiles, more than 350 years after it was conjectured. Our proof, which totals over 13 million lines of code, provides machine verification. More importantly, it proves over 29,000 other theorems that the proof requires, across many areas of math which had never before been formalized. We see this as a major step in the long process of firming up the core of mathematical knowledge, building on work from three centuries of mathematicians and hundreds of contributors to Lean and Mathlib. We are optimistic that AI-assisted verification of mathematical proofs will help reduce the burden of refereeing mathematics in an era where more proofs are being produced than ever before. You can read about the process on our Science Blog: https://www.anthropic.com/research/formalizing-fermats-last-theorem And see the complete proof on GitHub: https://github.com/anthropics/fermats-last-theorem
    @sammcallister“This extraordinary autoformalization achievement, which Anthropic researchers say only took 11 days, proves Fermat’s Last Theorem with no assumptions other than the axioms of mathematics. Along the way we see autoformalization of algebra, harmonic analysis, geometry and number theory, and we learn that AI autoformalization artefacts are now robust enough to be built upon; the proof is multi-layered.” https://www.anthropic.com/research/formalizing-fermats-last-theorem
    @Leonard41111588I did not expect this. Anthropic just published a Lean proof of Fermat's Last Theorem. The proof is +13M LoC, more than 5 times the size of Mathlib. Kevin Buzzard's post: https://xenaproject.wordpress.com/2026/09/04/flt-anthropic-has-beaten-me-to-it/ The proof: https://github.com/anthropics/fermats-last-theorem Anthropic's post: https://www.anthropic.com/research/formalizing-fermats-last-theorem
    @leanprover@AnthropicAI has shared the first end-to-end, computer-checked proof of Fermat's Last Theorem: 13 million lines of Lean, 29,500 intermediate theorems. Their announcement calls it "the largest Lean proof ever constructed." See also Kevin Buzzard's blog post about the proof: https://xenaproject.wordpress.com/2026/09/04/flt-anthropic-has-beaten-me-to-it/ 🔗 Anthropic's announce post: https://www.anthropic.com/research/formalizing-fermats-last-theorem 🔗 The code: https://github.com/anthropics/fermats-last-theorem #LeanLang #LeanProver #FLT
    @patrickshaftoRT @Leonard41111588: I did not expect this. Anthropic just published a Lean proof of Fermat's Last Theorem. The proof is +13M LoC, more th…
    @CsabaSzepesvari@AnthropicAI Old question, I will sound like a broken grammaphone: How do we know this formalization is correct? I would like to learn about the efforts made on this and a honest discussion of the limits of these efforts. Please please..
    @ShayneRedfordClaude formalized Fermat's Last Theorem in 11 days! 🚀 This spans 29k intermediate theorems, and 13M lines of Lean. For scale, Mathlib in it's entirety is ~8k files and 2.2M lines. This shows tremendous promise to automatically formalize massive swathes of modern mathematical literature, starting from the elementary vocabulary in Mathlib. Congratulations to @tianyi_peng who led this effort! https://www.anthropic.com/research/formalizing-fermats-last-theorem
    @nickcammarataimagine explaining to fermat that we had a guy in a computer write fourteen million lines of lean but we have a pretty good grasp on his conjecture now
    @allenainieThis is quite credible. I have read some of @tianyi_peng’s Markovian interference work, but this is absolutely mind blowing. It’s also a huge victory for decades of efforts in auto-formalization. AI is uplifted by years of human hard work.
    @patio11If you had told me in undergrad I’d love to see ~fully automatic formalization I would have bet against, and if you had told me that the machine doing it would have a running color commentary on the importance, I’d have thought you under the influence. https://www.anthropic.com/research/formalizing-fermats-last-theorem