OpenAI has granted nine major UK banks access to its GPT-5.5 Cyber model this week, offering lenders a powerful new cybersecurity tool after rival Anthropic restricted access to its Claude Mythos system, which UK banks have been unable to use.

The move gives institutions including Lloyds Banking Group, HSBC and Nationwide access to an AI model designed to identify software vulnerabilities and security weaknesses across complex digital systems. NatWest and Santander already had access through existing agreements, according to the BBC.

The rollout follows warnings from Bank of England governor Andrew Bailey last week that British banks remained unable to access Anthropic’s Mythos model to test the security of their own applications and infrastructure. The intervention highlighted growing concern within the financial sector over access to advanced AI-powered cybersecurity tools.

The UK’s AI Security Institute found that GPT-5.5 Cyber and Mythos reached “a similar level of performance” in cybersecurity tests, according to reports. Despite those findings, Anthropic has maintained tighter controls over Mythos, initially making it available to a group of around 42 companies, most of them US technology firms.

George Osborne, a senior OpenAI executive and former UK chancellor, told the BBC that the company did not want to “hide [5.5 Cyber] away or keep it to ourselves”, although access would remain restricted to approved organisations.

Osborne said: “The key things with these tools is that they need to be in the hands of the right people.”

He added: “We want to make sure that the forces that are establishing order in our democracies have these tools, and the forces that want to disrupt us or commit crime, do not.”

According to Anthropic, the company is working urgently to expand access to Mythos but believes the model’s capabilities require greater caution. The company argues that Mythos operates at a higher capability level than GPT-5.5 Cyber and therefore warrants additional safeguards.

The rollout reflects increasing competition between leading AI developers as banks and regulators seek technologies capable of identifying vulnerabilities in critical financial infrastructure.

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