Anthropic executive vows Japan cooperation on Mythos

Source: Nippon.com / Jiji Press Date: 2026-05-16 URL: https://www.nippon.com/en/news/yjj2026051501128/

Summary

Anthropic head of global affairs Michael Sellitto met LDP cybersecurity chief Masaaki Taira in Tokyo on May 16, pledging full cooperation with Japan’s measures against cyberattacks related to Claude Mythos. Japan’s government convened a public-private working group the previous day with major financial institutions and other stakeholders to coordinate cybersecurity responses. Mythos access remains restricted due to its vulnerability-finding capabilities.

Implications

First direct bilateral international engagement on Mythos outside the US legal/regulatory system. Japan’s rapid formation of a public-private working group signals that Mythos cybersecurity concerns are propagating through allied governments, not just US institutions (Pentagon, courts, CISA). Feeds the Mythos/Glasswing thread: the international dimension adds complexity to the supply chain risk designation — if allied nations want cooperation, the Pentagon exclusion becomes harder to sustain. Combined with the Anthropic supply chain appeal (oral arguments May 19), the governance picture is widening beyond US domestic politics.