Chinese AI ​startup Z.ai said on Friday its open-source GLM-5.3 model had neared Anthropic’s restricted Mythos 5 in identifying software vulnerabilities, bolstering the credentials of a Chinese ‌AI challenger gaining traction among Western developers. Z.ai said GLM-5.3 scored 84.5% on CyberGym, a test of whether a model can review code, identify security flaws and confirm that they are real. That was slightly higher than the 83.8% it reported for Mythos 5. The results have not been independently verified. GLM-5.3 lagged behind Mythos 5 in converting discovered flaws into working attacks — a standard part of defensive security research. Z.ai ​said its model scored 54.4% on the ExploitBench test of this capability, versus 78.0% for Mythos 5. In a separate timed test, Z.ai said GLM-5.3 completed 105 ​attack-development tasks in two hours and 130 in six hours. Mythos 5 completed 181 and 247 tasks, respectively.

Full report : Z.ai says GLM-5.3 scores 84.5% on CyberGym, vs. Mythos 5’s 83.8%, and its most sensitive cybersecurity functions will only be available to verified users.