The AI Security Institute, which has tested both Anthropic’s Mythos and OpenAI’s GPT-5.5 Cyber, said in its report that they reached “a similar level of performance” in the tasks it set them.
Last week Bank of England governor Andrew Bailey warned that UK banks were still unable to access Mythos to test the security of their own digital systems and apps.
Former UK Chancellor George Osborne, who is now a senior executive at OpenAI, told the BBC that Bailey had not contacted him directly. He said his firm did not want to “hide [5.5 Cyber] away or keep it to ourselves” but confirmed that, like Mythos, it would not become available to all.
“The key things with these tools is that they need to be in the hands of the right people,” he said.
“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.”
The UK banks which will now gain access to OpenAI’s GPT 5.5 Cyber include Lloyds Banking Group, HSBC and Nationwide. NatWest and Santander already have access under existing agreements.
The BBC has asked Anthropic whether it plans to grant UK financial institutions’ access to Mythos.
Anthropic initially opened it up to a collective of 42 companies, mostly other US tech firms.