LLM-discovered zero-days (Opus 4.6)
Released with Opus 4.6, Anthropic reports Claude found and validated more than 500 high-severity vulnerabilities in well-tested open-source software with no custom scaffolding.
Opus 4.6 reasoned about code like a human researcher (reading past fixes, spotting bug patterns) rather than fuzzing, finding long-undetected bugs in projects with years of fuzzer time. Anthropic began reporting and patching them with maintainers and described the misuse safeguards it added.
- Date
- Thursday, 5 February 2026
- Lab
- Anthropic
- Kind
- paper
- Access
- paper only
Figures
| Measure | Value | Measured by |
|---|---|---|
| High-severity vulnerabilities found and validated | more than 500 in open-source software, human-validated before reporting | company |
Precursor to Claude Code Security (2026-02-20), the Mozilla collaboration and Mythos Preview.
Sources
This record was checked against its sources on 6 October 2026. How we check