Z.ai GLM-5.3 nears Anthropic Mythos 5

Chinese AI startup Z.ai announced on August 14, 2026 that its open-source GLM-5.3 model had neared Anthropic's restricted Mythos 5 in identifying software vulnerabilities. Z.ai reported GLM-5.3 scored 84.5% on CyberGym, slightly higher than the 83.8% it reported for Mythos 5, though results were not independently verified. However, GLM-5.3 lagged behind Mythos 5 in converting flaws into working attacks, scoring 54.4% on ExploitBench versus 78.0% for Mythos 5. Z.ai plans to release GLM-5.3 publicly in about two weeks after security assessments, with sensitive cybersecurity functions available only to verified users through a 'trusted access' program. The company framed the launch as a challenge to closed-source models, arguing advanced cyber-defense tools should be accessible to open-source developers and smaller security teams. It also announced an 'Open Source Shield' initiative to audit open-source projects and provide model access for defensive work. The launch builds on interest in GLM-5.2, which gained traction among overseas developers for coding and agent capabilities approaching leading U.S. models at lower cost.