Mythos

A month after its initial release, a newer checkpoint of Anthropic's Mythos Preview became the first model to complete the UK AI Safety Institute's 'Cooling Tower' cyber range, solving it in 3 of 10 attempts. The model also completed 'The Last Ones' range in 6 of 10 attempts, surpassing OpenAI's GPT-5.5 and demonstrating capability improvements within a single model version.

OpenAI has launched Daybreak, a cybersecurity platform built on three GPT-5.5 model variants designed to detect software vulnerabilities, generate patches, and validate fixes in enterprise codebases. The platform directly competes with Anthropic's Mythos and includes partnerships with eight major security companies including Cisco, Cloudflare, and CrowdStrike.

OpenAI announced GPT-5.5-Cyber is rolling out in limited preview to vetted cybersecurity teams and is in discussions with the European Commission about preview access. Anthropic released its Mythos model a month ago but has yet to grant EU access for security review.

OpenAI is providing a less-restricted version of GPT-5.5 to vetted cybersecurity defenders through its Trusted Access for Cyber program. The model, dubbed GPT-5.5-Cyber, completed a 32-step simulated corporate cyberattack in 2 out of 10 test runs according to the U.K. AI Security Institute, narrowly trailing Anthropic's Mythos which succeeded in 3 out of 10 attempts.

Mozilla's Firefox team reports that Anthropic's Mythos model has discovered thousands of high-severity security vulnerabilities, including bugs that had remained undetected for more than 15 years. In April 2026, Firefox shipped 423 bug fixes compared to just 31 in April 2025, marking a 13x increase attributed to AI-assisted vulnerability detection.

The National Security Agency is using Anthropic's Mythos Preview, an unreleased cybersecurity model limited to roughly 40 organizations, according to Axios. The deployment comes weeks after the Department of Defense labeled Anthropic a "supply chain risk" following the company's refusal to grant Pentagon officials unrestricted access to its models.

Anthropic released Claude Opus 4.7 with improved coding capabilities, higher-resolution vision, and a new reasoning level. The company publicly acknowledged the model underperforms its unreleased Mythos system, which remains restricted due to safety concerns.

OpenAI released GPT-5.4-Cyber, a model variant designed for defensive cybersecurity tasks with fewer restrictions on dual-use queries. Access is controlled through a tiered verification system in the Trusted Access for Cyber program, targeting thousands of vetted users compared to Anthropic's 40-organization Mythos Preview rollout.

Federal Reserve Chairman Jerome Powell and Treasury Secretary Scott Bessent met with major U.S. bank CEOs this week to assess cyber risks from Anthropic's newly released Mythos model. Anthropic deployed Mythos in limited capacity due to concerns that hackers could exploit its capabilities.