Cybersecurity vets protest ‘dangerous’ US government ban on Anthropic’s most powerful models

The U.S. government ordered Anthropic to restrict exports of its Fable and Mythos AI models (advanced models designed to find security vulnerabilities), citing national security concerns, which prompted Anthropic to suspend worldwide access to these models. Dozens of prominent cybersecurity experts published an open letter arguing this ban is dangerous because it removes powerful security tools from defenders while adversaries continue advancing, and they claim the vulnerability that justified the ban can be replicated in other widely available AI models like OpenAI's GPT-5.5 and Claude Opus 4.8.