OpenAI Grants Japan's Megabanks Access to GPT-5.5 for Cyber Defence

Japan's Banks Gain Frontier AI for Cyber Defence

Japanese Finance Minister Satsuki Katayama announced on Friday that OpenAI has granted select Japanese financial institutions access to its GPT-5.5 model to bolster their defences against cyberattacks. The announcement followed a meeting in Tokyo with OpenAI Chief Strategy Officer Jason Kwon. Without naming specific institutions, Katayama described the access as "a big step forward in strengthening Japanese financial institutions' ability to defend against cyberattacks."

Who Benefits

The Nikkei newspaper reported on 28 May that Japan's three largest banks — MUFG Bank, Sumitomo Mitsui Banking Corp, and Mizuho Bank — are expected to gain access to the model. The banks have not independently confirmed the arrangement. The model, referred to as GPT-5.5-Cyber, is being delivered through OpenAI's "Trusted Access for Cyber" programme, a framework designed to ensure only verified defenders can use the tool.

What It Enables

According to reporting via Morningstar, the model could allow Japan to better scrutinise systemic risks, identify gaps in information security, and implement countermeasures. The thinking is that the same frontier AI systems capable of powering more sophisticated cyberattacks must also be deployed defensively, giving institutions a way to spot vulnerabilities before attackers exploit them.

A Broader Pattern

The decision followed discussions between the Japanese and U.S. governments and mirrors a similar agreement previously reached with European companies. Katayama also said Japan's government and financial institutions were expected to gain access to Anthropic's Claude Mythos model to further enhance their defences. The Nikkei reported that GPT-5.5 is believed to be comparable in capability to Mythos, which is currently limited to roughly 50 companies worldwide. Some Japanese financial firms will also gain access to Mythos following approval from the Trump administration.

Why It Matters

The move reflects a growing recognition among regulators that advanced AI cuts both ways. "With frontier AI now recognised as a threat, this step could serve as a welcome catalyst to strengthen cybersecurity within Japan's financial sector," Katayama told reporters. It sits within a wider wave of activity, including Google Cloud's launch of an autonomous threat defence platform, the European Central Bank urging banks to boost cyber investment, and a G7 agreement to bolster shared financial defences against AI-powered attacks.