Anthropic just split its most advanced AI model into two distinct products, and the dividing line is cybersecurity. Claude Mythos 5, the full-power version capable of discovering and exploiting software vulnerabilities, remains restricted to vetted organizations. Claude Fable 5, the public and enterprise variant launched on June 9, 2026, ships with safety guardrails firmly in place and the cyber-offense toolkit stripped out.
Two models, very different access levels
Mythos 5 represents a major leap in AI-driven vulnerability research. The model builds on the Mythos Preview released in April 2026, with substantial gains in its ability to identify and exploit software flaws. During an initial testing phase called Project Glasswing, around 40 organizations were given limited access to evaluate the model’s capabilities. The results were apparently compelling enough that Anthropic expanded the program before settling on the restricted-access commercial launch.
Fable 5, meanwhile, is the version most people will actually interact with. It retains the model’s general reasoning and coding abilities but comes without the full suite of cybersecurity features. It can help you write code, analyze data, and handle complex reasoning tasks, but it won’t help you find zero-day exploits in production software.
