Anthropic says Zhipu's open-weight GLM-5.3 nearly matches Claude Mythos Preview at building exploits

Zhipu's open-weight model GLM-5.3 comes close to Claude Mythos Preview at exploit development, according to an Anthropic analysis. Anthropic says the model's safeguards can be bypassed with simple methods. The company also has its own reasons to sound the alarm. Five months after Anthropic unveiled Claude Mythos Preview, its Frontier Red Team says the model's signature capability has reached the competition.

In a new analysis, the team looks at GLM-5.3 from Zhipu AI, which operates as Z.ai outside China. According to Anthropic, GLM-5.3 can build complete cyber exploits on its own, just like Mythos Preview. Unlike every other model with comparable skills, though, it shipped without effective safeguards. Anthropic deliberately held Mythos Preview back, giving access only to select defenders through Project Glasswing so they could get a head start.

The company says those defenders have since found more than 10,000 vulnerabilities in critical software. OpenAI is taking a similar approach with Daybreak. GLM-5.3, on the other hand, is available for anyone to download. ExploitBench measures how well models exploit known bugs in Chrome's V8 engine. On that benchmark, GLM-5.3…