Anthropic launches Claude Opus 5.5 with stricter safeguards for cybersecurity

Anthropic says its new Claude Opus 5.5 model comes with stronger safeguards in the wake of recent rogue AI hacking incidents. In an announcement on Tuesday, Anthropic says Opus 5.5 comes with improvements to certain risky behaviors, including attempts to escape the company’s testing sandbox.

It’s the first model released by Anthropic after CEO Dario Amodei announced plans to “pace the frontier,” or slow down AI development. In recent weeks, several AI companies, including Anthropic, Google, and OpenAI, have reported that their AI models escaped containment and hacked third-party companies during testing.

Anthropic says Opus 5.5 is the “strongest-performing” model on the company’s most comprehensive alignment test. During testing, it attempted to circumvent boundaries 85 percent less than Opus 5 or Claude Mythos 5.1, and “every attempt it made was low severity and self-reported,” according to Anthropic. It also comes with improvements to biased or motivated reasoning, which contributed to recent AI hacks.

Opus 5.5 costs 40 percent less to run than Opus 5, but matches the performance of Fable 5.1 “on most work.” It also comes with safeguards similar to the ones offered by Anthropic’s more advanced Fable 5.1 model. That means Opus 5.5 will re-route certain cybersecurity-related requests to the less powerful Opus 4.8, while biology-related requests flagged by its safeguards will go to Opus 5.

Anthropic says Opus 5.5 was tested by outside partners, including Frontier Design and METR, before release. The company also plans to launch Claude Sonnet 5.5 and Haiku 5.5 in the coming weeks.

Update, September 22nd: Added more information from Anthropic’s blog.