White House Bars UK AI Safety Institute From Testing New OpenAI and Anthropic Models

The White House has ordered OpenAI and Anthropic to withhold new frontier models from the UK's AI Security Institute until US reviews are complete. Anthropic complied: Claude Mythos 5.1 launched September 1 only for US organizations. Reviews now route through CAISI, which has had no permanent director for 67 days.

• Anthropic released Claude Mythos 5.1 on September 1 only to US organizations
• CAISI has lacked a permanent director for 67 days and has only dozens of staff
• In June 2026 Commerce forced Anthropic to pull Claude Fable 5 and Mythos 5 globally
• UK AISI was excluded from a pre-release Anthropic evaluation for the first time