Yes, as of September 2026. Anthropic's Frontier Red Team tested GLM-5.3 from Zhipu AI (known outside China as Z.ai) and wrote that "like Claude Mythos Preview, GLM-5.3 has strong capabilities for autonomously building end-to-end cyber exploits." GLM-5.3 is an open-weight model. Anyone can download it and run it. Anthropic's conclusion: "a critical threshold in freely accessible capabilities has now been crossed."
What the tests showed:
- Exploit building. On ExploitBench, a public benchmark built on known flaws in the V8 engine inside Google Chrome, GLM-5.3 built a working end-to-end exploit in 50 of 410 attempts. Claude Mythos Preview did it in 56. On Anthropic's internal binary exploitation test GLM-5.3 scored 4% and Mythos Preview 6%.
- Cost of a real attack. A researcher gave GLM-5.3-Flash, a smaller version, the public details of a recently fixed Chrome flaw. It produced a working attack. At Zhipu's API prices that work would have cost $20.40.
- Safeguards. A plain attack request is often refused. A cover story (telling it that it is a red-team agent on an exercise) gets it to go ahead 64% of the time. Prefilling its reasoning gets 92%. A copy with the refusals edited out gets 100%.
- Removing the refusals. The edit is called abliteration. Anthropic's team did it on the first try for about $4,400 of computing, and the model kept most of its ability. Other developers had published edited copies within days of the release.
The independent check. On 17 September 2026 NIST's Center for AI Standards and Innovation (CAISI) called GLM-5.3 "the most cyber-capable open-weight model released to date" and put it about four months behind the US frontier: CAISI's assessment. Anthropic says its findings broadly match.
Why the download matters. Mythos Preview went only to vetted defenders through a trusted access programme. A downloadable model has no such gate. Anthropic also points out that the same capability helps defenders find and fix flaws first.
Source: Anthropic, GLM-5.3 and the spread of advanced cyber capabilities. The wider picture of AI and cyber risk in 2026 is in is AI making cyber attacks worse?. Full write-up with the deck: https://www.tigzig.com/post/anthropic-glm53-open-weight-cyber-sep2026.
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