OpenAI Launches GPT-5.4-Cyber for Defensive Security Teams — Fine-Tuned Frontier Model for Vulnerability Hunting

The Hacker News·high signal

OpenAI unveiled GPT-5.4-Cyber on April 14, a variant of GPT-5.4 fine-tuned for defensive cybersecurity, days after Anthropic's Mythos release. The model is being distributed through the expanded Trusted Access for Cyber (TAC) program to thousands of authenticated individual defenders and hundreds of security teams. It has already helped identify 3,000+ vulnerabilities in production software — this is OpenAI's clearest move yet to compete with Anthropic's security-focused Mythos deployments.