GPT-5.5-Cyber is a specialized cybersecurity model built for advanced defenders who need deeper capability and more flexible support for authorized security work. The updated model is designed to reduce unnecessary refusals while improving performance on vulnerability discovery, validation, patch development, and remediation workflows. It can analyze large codebases, identify security-relevant components, determine whether vulnerable code is reachable, validate likely issues in controlled environments, and help prepare evidence for human review. GPT-5.5-Cyber is intended to move defenders through the full remediation process, from finding a vulnerability to testing and supporting a fix. The model retains the general-purpose intelligence of GPT-5.5 while adding stronger cyber-specific performance for complex, long-running tasks. Benchmark results show higher scores than GPT-5.5 on CyberGym, ExploitGym, and SEC-bench Pro, including stronger single-model performance in reproducing known vulnerabilities and evaluating complex software targets. GPT-5.5-Cyber is positioned for verified defenders whose work requires advanced cyber capabilities and more permissive behavior than standard access models. Its deployment approach includes stronger verification, monitoring, scoped controls, and review to support responsible use. GPT-5.5-Cyber helps security teams identify actionable issues, reduce noise, validate findings, and land safer fixes across demanding software security workflows.