Anthropic’s Claude Mythos Preview has become the first AI model to complete a full simulated corporate network attack, according to new evaluations from the UK’s AI Security Institute (AISI).
The findings, published days after the model’s April 7 announcement, suggest AI cyber capabilities have reached a level that demands immediate attention from security teams worldwide.
What Is Claude Mythos?
Anthropic unveiled its Claude Mythos Preview model on April 7, opting against a broad public release. The team instead grants limited access to security research firms to evaluate and prepare for its advanced capabilities.
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The development has already begun to draw attention across tech and even policy circles. According to a Reuters report citing sources familiar with the matter, US Treasury Secretary Scott Bessent and Federal Reserve Chair Jerome Powell held an urgent meeting with major bank CEOs, warning about potential cyber risks linked to this model.
How Claude Mythos Preview Performed
AI Security Institute (AISI), a research organisation within the UK government’s Department for Science, Innovation and Technology, conducted cyber evaluations of Anthropic’s Claude Mythos Preview to examine its cybersecurity capabilities.
First were the capture-the-flag (CTF) evaluations, where systems must identify and exploit vulnerabilities to retrieve hidden “flags.” Mythos achieved a 73% success rate on expert-level tasks. This had remained unsolved by any model prior to April 2025.
Claude Mythos Cyber Attack Capabilities. Source: AISIMoreover, AISI built a 32-step corporate network attack simulation called “The Last Ones” (TLO). Human security professionals would need roughly 20 hours to finish it.
Mythos Preview finished the entire simulation in 3 out of 10 attempts. On average, it completed 22 of the 32 attack steps. Claude Opus 4.6, the next-best performer, averaged only 16 steps.
Anthropic’s own red team testing found that Claude Mythos Preview can detect and exploit zero-day vulnerabilities across all major operating systems and leading web browsers when explicitly instructed by a user.
AISI noted that organizations should prioritize foundational cybersecurity measures. These include regular patching, strict access controls, security configuration hardening, and comprehensive logging.
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The post Claude Mythos Cracks 73% of Expert Cyber Tasks No AI Could Solve Before appeared first on BeInCrypto.
Source: https://beincrypto.com/claude-mythos-preview-cyber-capabilities-test/
