CAISI: GLM-5.3 is the most cyber-capable open-weight model yet
A US government eval puts an open-weight model's exploit skills well below frontier models, but ahead of other open weights.
· NIST CAISI · Research by Center for AI Standards and Innovation (CAISI) (NIST)
NIST's Center for AI Standards and Innovation rates Z.ai's GLM-5.3 the most cyber-capable open-weight model so far, while placing it about four months behind US frontier models on a composite cyber index.
01What happened
NIST's Center for AI Standards and Innovation (CAISI) published its assessment of Z.ai's GLM-5.3 on September 17, 2026. CAISI calls it the most cyber-capable open-weight model released to date, and says it is significantly lower than US frontier models, about four months behind on a composite index.
02How it works
CAISI ran GLM-5.3 as an agent with bash and Python tools on four benchmarks: SEC-Bench Pro, ExploitBench, ExploitGym Userspace and a private OSS-Fuzz set. GLM-5.3 scored 40.4% on SEC-Bench Pro against 90.2% for a US frontier model, and 61.1% on ExploitBench against 100%. CAISI combines results into an item response theory index, where +400 points means ten times the odds of solving a task.
03Who is affected
Defenders whose threat models assume attackers lack strong exploit-development help. GLM-5.3 has open weights, so anyone can download and run it without access controls.
04What to do
Assume capable, freely downloadable exploit-writing assistance is available to attackers, and shorten patch timelines for known vulnerabilities accordingly.
Sources 2 links, all fetched
- 1nist.govCAISI Assessment
- 2anthropic.comAnthropic Analysis