Building AI for cyber defenders

This post details the enhancement of Claude's cybersecurity capabilities, specifically for defensive applications. It highlights the development of Claude Sonnet 4.5, which demonstrates significant improvements in vulnerability discovery and patching. The work involved focused research on code vulnerability discovery, patching, and testing for weaknesses in simulated deployed security infrastructure, deliberately avoiding enhancements favoring offensive work. The post presents evaluation results from Cybench and CyberGym, showing substantial improvements in vulnerability detection rates and the ability to discover new vulnerabilities. Preliminary research into patch generation and review is also discussed, with initial results indicating that generated patches can be semantically equivalent to human-authored ones. Real-world feedback from organizations like HackerOne and CrowdStrike is included to validate the practical impact of these advancements.