OpenAI on Tuesday unveiled GPT-5.4-Cyber, a variant of its latest flagship model fine-tuned specifically ​for defensive cybersecurity work, following rival Anthropic's ‌announcement of frontier AI model Mythos.

Mythos, announced on April 7, is being deployed as part of Anthropic's "Project ​Glasswing," a controlled initiative under which select ​organizations are permitted to use the unreleased Claude Mythos Preview model for defensive cybersecurity purposes. ​It has found "thousands" of major vulnerabilities in operating ​systems, web browsers and other software.

OpenAI, creator of popular chatbot ChatGPT, said that GPT-5.4-Cyber will initially be rolled out on a limited basis to vetted security vendors, organizations and researchers because of its more permissive ‌design.

The company is also expanding its Trusted Access for Cyber program to thousands of verified individual defenders and hundreds of teams protecting critical software, it said in a post on its website.

OpenAI is adding new tiers to its TAC program, which was launched in February, with higher levels of verification unlocking more powerful capabilities.

Users approved for the highest tier will gain access to GPT-5.4-Cyber, which ​has fewer restrictions on ​sensitive cybersecurity tasks such as vulnerability research and analysis.