Anthropic says its Claude model has formally verified security properties in 123 open-source software libraries, uncovering hundreds of bugs during the process. Some flaws had escaped detection for years, despite trillions of automated test runs.

The project, conducted with software verification firm Theorem, applies mathematical proofs directly to compiled machine code. Researchers say the approach could make rigorous software verification practical for a much wider range of projects.

The work targets a growing security problem. Automated tools can now discover vulnerabilities in mature software, leaving developers searching for stronger ways to prevent exploitable flaws. Formal verification offers a potential answer by proving that code follows specific rules under defined conditions.

Traditional software testing runs programs against selected inputs to expose failures. Fuzzing tools generate large numbers of unusual inputs, but they cannot exhaust every possible combination.

Anthropic used Claude to turn existing fuzz tests into mathematical specifications. The model then generated proofs showing that 239 program entry points across 123 libraries would not crash under defined conditions.

The researchers worked with RISC-V assembly code, which represents instructions executed by a processor. Claude generated roughly 180 million lines of proof code, with a typical proof spanning about 600,000 lines.

A separate tool called Rocq checked the proofs against their specifications. This independent verification step means developers do not need to manually inspect every line of generated proof code. Anthropic also allowed Claude to patch bugs discovered during verification. The model then generated new proofs for the updated code.

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