The UK’s biggest banks have a cybersecurity AI problem, and OpenAI is trying to be the solution. The company has offered nine UK financial institutions access to its GPT-5.5-Cyber model, a move that comes while those same banks remain locked out of Anthropic’s Claude Mythos Preview, the model widely considered the most capable cyber-offense simulator on the market.
Bank of England Governor Andrew Bailey confirmed that as of May 29, 2026, UK banks still lack access to Anthropic’s Mythos AI model. That’s nearly two months after Mythos Preview launched in early April, and the delay has created what amounts to a defensive blind spot for institutions managing trillions in assets.
The cyber arms race between OpenAI and Anthropic
Anthropic’s Claude Mythos Preview, released around early April 2026, demonstrated remarkable efficiency in executing complex cyber-attack simulations. It became the first model to successfully complete what’s described as a comprehensive corporate network attack simulation, essentially threading through layered defenses the way a sophisticated threat actor would.
OpenAI’s GPT-5.5-Cyber entered the picture on May 7, 2026, when the company rolled out access to verified defenders in critical infrastructure sectors through its Trusted Access for Cyber program, or TAC. The UK’s AI Security Institute evaluated GPT-5.5 and found it to be one of the strongest models available for cyber-related tasks. In AISI’s assessment, GPT-5.5 became the second model to successfully navigate a corporate network attack simulation, trailing only Mythos Preview.
