OpenAI releases GPT-5.5-Cyber, a less-restricted AI variant for authorized security researchers testing vulnerabilities

OpenAI is giving security researchers access to GPT-5.5 through a tiered system: a public model with standard restrictions, a middle tier with relaxed filters for defensive work, and GPT-5.5-Cyber with the fewest restrictions for authorized penetration testing. Starting June 1, 2026, individual users on the highest access tier will need to enable phishing-resistant authentication.

GPT-5.5-Cyber performs roughly on par with Anthropic's Mythos Preview when it comes to finding and exploiting software vulnerabilities. In tests by the UK's AI Security Institute simulating a corporate network attack involving 32 steps, GPT-5.5 completed the full chain in 2 out of 10 runs, while Mythos managed 3 out of 10.

Launch partners for the program include Cisco, CrowdStrike, Palo Alto Networks, Cloudflare, Intel, Snyk, and SentinelOne. Select developers working on major open-source projects also get discounted access through Codex Security.