In April, OpenAI launched GPT-5.4 Cyber and rolled it out to a limited number of vetted security organisations, researchers, and vendors, providing them with an alternative to Mythos.
“We want to empower defenders by giving broad access to frontier capabilities, including models which have been tailor-made for cyber security,” OpenAI said.
“This is a version of GPT‑5.4 which lowers the refusal boundary for legitimate cyber security work and enables new capabilities for advanced defensive workflows, including binary reverse-engineering capabilities that enable security professionals to analyse compiled software for malware potential, vulnerabilities and security robustness without needing access to its source code.”
Now, the company has offered UK and Japanese banks access to the next iteration, GPT-5.5 Cyber, for use in cyber defence, an offer that Japan has taken the company up on.
Japan’s Finance Minister Satsuki Katayama said the offer was accepted after talks in Tokyo with OpenAI chief strategy officer Jason Kwon, adding that early access to the model will allow them to gain a hold against cyber criminals using advanced strategies and AI technology.
While Katayama did not name the financial institutions involved, she said that the move was “a big step forward in strengthening Japanese financial institutions’ ability to defend against cyber attacks”.
That being said, Katayama also said that both the Japanese government and the nation’s financial institutions expected to gain access to Mythos.
OpenAI also offered GPT-5.5 access to nine major UK banks, as Anthropic denied them access to Mythos. Banks include Lloyds Banking Group, HSBC, and Nationwide. Existing agreements mean that Santander and NatWest already have access.
Former UK chancellor and senior OpenAI executive George Osborne said the AI firm did not want to hide GPT-5.5 away but maintained it would not be 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.”
While the Bank of England governor warned that UK banks still lacked Mythos access, an Anthropic spokesperson told media that the company was working hard to expand Mythos access, adding that they believe that Mythos has greater capabilities with GPT-5.5 and that this needs to be handled more carefully.
However, the AI Security Institute, which has tested both GPT-5.5 and Mythos, said they reached “a similar level of performance” in the benchmarking tests it ran.
Anthropic has provided Mythos access to 42 companies to date, most of which are other US tech firms, while OpenAI has provided access to EU and Canadian banks, and now the UK and Japan.
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