Cybersecurity researchers have found significant vulnerabilities in models from both Anthropic and OpenAI, with the fallout now reaching the highest levels of the US government.
A report from FAR.AI tested multiple frontier models, including Anthropic’s Claude Opus 4.8, Fable 5, and OpenAI’s GPT 5.5 and 5.6, and found them susceptible to jailbreak attacks designed to extract genuinely dangerous outputs, including exploitative code, chemical weapons information, and biological weaponry details.
The numbers tell a damning story
Anthropic and OpenAI’s models weren’t the worst performers. That distinction belongs to xAI’s Grok models, which logged 448 instances of successful automated jailbreaks. Google’s Gemini models came in second at 249 instances. Claude, Fable, and GPT series models showed comparatively greater resistance to jailbreaking.
In June 2026, the Commerce Department restricted foreign access to Anthropic’s Fable 5 and Mythos 5 models after a reported jailbreak technique surfaced. The White House has also requested that both OpenAI and Anthropic delay the release of certain upcoming models so the government can properly assess cybersecurity risks.
