Chinese startup z.ai has released GLM-5.3, a new open-source language model, through its API. This advanced model reportedly found a vulnerability in Cursor and offers strong coding and agent performance. Developers can now build applications using GLM-5.3, with its API pricing remaining the same as its predecessor, GLM-5.2. The input tokens cost $1.40 per million, and output tokens cost $4.40 per million. Despite identical per-token rates, GLM-5.3 may incur higher overall costs due to increased verbosity. GLM-5.3's performance places it among the top open-weight models, tying with Kimi K3 on the Intelligence Index. However, it is not the cheapest option available, with models like Google's Gemini and OpenAI's GPT-5.6 Luna offering lower introductory prices. Z.ai plans to make the model's weights openly available, but a specific date and licensing are pending. The API access is currently limited to a protocol compatible with OpenAI's Chat Completions for existing GLM Coding Plan subscribers. This release provides developers with a more powerful, yet relatively cost-effective, choice for advanced AI tasks.