Models of this capability level require stronger cyber safeguards before they can be generally released.

We are treating the biological/chemical and cybersecurity capabilities of GPT‑5.5 as High under our Preparedness Framework. While GPT‑5.5 didn't reach Critical cybersecurity capability level, our evaluations and testing showed that its cybersecurity capabilities are a step up compared to GPT‑5.4.

We are treating the biological/chemical and cybersecurity capabilities of GPT‑5.5 as High under our Preparedness Framework. While GPT‑5.5 didn't reach Critical cybersecurity capability level, our evaluations and testing showed that its cybersecurity capabilities are a step up compared to GPT‑5.4.

We are treating the biological/chemical and cybersecurity capabilities of GPT‑5.5 as High under our Preparedness Framework. While GPT‑5.5 didn't reach Critical cybersecurity capability level, our evaluations and testing showed that its cybersecurity capabilities are a step up compared to GPT‑5.4.

The group accessed Mythos by using knowledge of Anthropic’s other model formats obtained from a recent [Mercor data breach](https://www.theverge.com/ai-artificial-intelligence/907083/a-company-that-makes-ai-training-data-has-been-hit-by-a-security-breach) to make “an educated guess” about its online location.

For the computer-use work that sits at the heart of XBOW's autonomous penetration testing, the new Claude Opus 4.7 is a step change: 98.5% on our visual-acuity benchmark versus 54.5% for Opus 4.6.

Anthropic found that Mythos Preview was far more capable than previous models at exploiting vulnerabilities in Firefox's JavaScript implementation. Anthropic's previous best model, Claude Opus 4.6, created a successful exploit less than 1% of the time. Mythos Preview did so 72% of the time.

Deepfake scams have stolen tens of millions. AI-generated phishing bypasses legacy filters.

Out of all generated PoCs, 759 triggered crashes across 60 projects, and manual inspection confirmed 17 cases of incomplete patches spanning 15 projects

Mythos Preview has already found thousands of high-severity vulnerabilities, including some in every major operating system and web browser.

Claude Mythos autonomously identified and exploited several significant vulnerabilities. Notably, it discovered a 27-year-old vulnerability in OpenBSD

In the past, exploiting an application required a highly skilled hacker with years of experience and a significant investment of time to find and exploit vulnerabilities.