According to Sina Finance, citing people familiar with the matter, Anthropic refused to submit its latest model to the UK AI Safety Institute for testing before release. Claude Mythos 5.1 is available only to vetted U.S. institutions and was not provided to the UK AI Safety Institute. The report, citing UK government data, said the decision raised concerns inside Whitehall and the institute. Anthropic declined to comment. The UK Cabinet Office said the AI Safety Institute "continues to work closely with industry partners, including Anthropic, to improve model safety."