Japan banks get OpenAI GPT-5.5 access to bolster cyber defences

Japanese finance minister Satsuki Katayama said several Japanese financial institutions and government bodies have been granted restricted access to OpenAI’s GPT-5.5 (comparable to Anthropic’s Mythos) to strengthen cyber defences. The move, following talks with OpenAI and discussions between Tokyo and Washington, aims to help banks detect vulnerabilities and counter AI-enabled cyber threats. Authorities have set up a public‑private working group to assess Mythos‑linked risks. Market impact: this should reduce operational and cybersecurity risk for major Japanese banks, potentially lowering sector risk premia and modestly supporting investor confidence in Japan‑listed financials and broader indices such as the Japan 225, while keeping regulatory scrutiny and coordination with global partners in focus.