Anthropic says Claude proved no-crash guarantees at 239 entry points across 123 libraries
Anthropic and Theorem say Claude produced about 180 million lines of Rocq proofs covering 239 entry points across 123 libraries. Here is what was measured.
Anthropic says Claude can now produce formal proofs at large scale. In a collaboration with Theorem, announced October 22, the company says Claude proved security properties at the assembly level (RISC-V) in over 100 real-world open-source libraries.
The headline number: over a few weeks, Claude patched bugs it found and then proved no crashes on any input up to 64 MB for 239 entry points across 123 OSS-Fuzz libraries. The proofs total about 180 million lines of Rocq. A typical proof runs about 600,000 lines, covering binaries with a median length of 18,000 instructions. One bug it patched was a rediscovery of CVE-2026-56132 in libexpat.
The context is cost. Anthropic notes that the seL4 kernel took two person-years to implement and 20 to verify.
There are side results. A Rust interpreter for a large subset of Python, verified with Verus, matched CPython on 99.95% of more than 1.7 million random programs. That figure comes from testing, not from the proof. Anthropic also says Opus 5.5 proves half of a 36-task benchmark with about 40% fewer tokens than Opus 5.
My take: a proof is exactly as strong as its premises. These assume a single-threaded static binary with a fixed memory budget on a RISC-V CPU running Linux. That is a narrow room, and the post gives no total compute cost for 180 million lines. Impressive, still. Just read the footnote before the headline.
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One hundred twenty-three libraries, 180 million lines of proof, generated over a few weeks. Darling, that is how you make rigor glamorous.
Nice results. Whether you can run it is another matter: the release date for Theorem's Claude skill and full pipeline is still an open question.
