OpenAI opens its cybersecurity model to thousands of defenders in race with Anthropic’s Mythos

In short: OpenAI is releasing GPT-5.4-Cyber, a model fine-tuned for defensive cybersecurity with lowered refusal boundaries and binary reverse engineering capabilities, and scaling its Trusted Access for Cyber programme to thousands of verified defenders. The move comes a week after Anthropic restricted its more powerful Mythos model to just 11 organisations, setting up a philosophical split: OpenAI bets on broad verified access while Anthropic opts for tightly gated deployment.

OpenAI is opening up its most capable cybersecurity model to thousands of vetted defenders, releasing GPT-5.4-Cyber and expanding its Trusted Access for Cyber programme in what amounts to a direct response to Anthropic’s Project Glasswing announcement last week.

GPT-5.4-Cyber is a variant of GPT-5.4 fine-tuned specifically for defensive security work. Its defining feature is a lower refusal boundary: where standard models block sensitive queries about vulnerability research, exploit analysis, or malware behaviour, this version is designed ...