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

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

Users will find Opus 4.8 to be a modest but tangible improvement on its predecessor. There’s still more to be done: we’re working on developing and releasing models that provide many of the same capabilities as Opus at a lower cost. Not only that, but we plan to release a new class of model with even higher intelligence than Opus. As part of Project Glasswing, a small number of organizations are currently using Claude Mythos Preview for cybersecurity work. Models of this capability level require stronger cyber safeguards before they can be generally released. We’re making swift progress on dev