Claude Mythos

Anthropic said Claude Fable 5 is the safer version of Claude Mythos 5, which only trusted cybersecurity and software professionals should have access to through Anthropic's Project Glasswing program. The Fable model has cybersecurity protections that Mythos doesn't have. "Fable 5 complied with zero harmful single-turn requests relating to planning a cyberattack, exploit development or defense evasion," the company said. "This held whether or not one of the requests used any of 30 different public jailbreak techniques." AI-enabled bioterror -- a horrifying phrase and even scarier reality -- has

The Associated Press dug deeper, and was informed by an unidentified US official that Mythos merely found vulnerabilities within hours, not necessarily exploited them. Still, identifying a vulnerability that theoretically can be exploited for attacks against protected US Government systems should be cause for concern on its own. Mythos is an advanced AI model built by Anthropic, first introduced in early April this year. However, the company decided not to share it with the general public because it was apparently too capable of discovering and leveraging software vulnerabilities. Instead, Ant

Withholding a model has been a long-standing lever in Frontier Lab safety plans. Before Mythos Preview and Glasswing, OpenAI launched their Trusted Access for Cyber program for GPT-5.3-Codex (their first model to reach “High” cybersecurity capability). Anthropic have now launched their similar Cyber Verification Program.

The UK AI Security Institute (AISI) put it best with this summary, “Mythos Preview represents a step up over previous frontier models in a landscape where cyber performance was already rapidly improving”. The AISI recently created an evaluation which tests model capability on a network attack simulation spanning 32 stages of an attack chain (estimated to take a human 20 hours to complete). Mythos Preview is the first model to solve this challenge from start to finish, succeeding on 3 of 10 attempts with a 100 million token budget. AISI expect greater budget would improve results further. Mytho