LLMs are Getting a Lot Better and Faster at Finding and Exploiting Zero-Days

Claude Opus 4.6, a new AI model, is significantly better at finding zero-day vulnerabilities (security flaws unknown to vendors and the public) than previous models, discovering high-severity bugs in well-tested code that fuzzing tools (programs that test software by sending random inputs) had missed for years. Unlike traditional fuzzing, Opus 4.6 analyzes code like a human researcher would, studying past fixes and code patterns to reason about what inputs would cause failures.