GLM-5.3: the flagship for hard problems

GLM-5.3 was listed on OpenRouter on 18 August 2026. Its model card is direct about where it comes from: GLM-5.3 uses the same base model as GLM-5.2, and "every gain comes from post-training". In other words, Z.ai did not change the architecture; it trained the model to be much better at complex coding and long tasks.

Z.ai reports a 50% improvement over GLM-5.2 on its in-house Z.ai Code Bench and claims open-source state-of-the-art results on public benchmarks such as Terminal Bench 3.0 and Agents' Last Exam. The card also notes an emergent strength in security research, with state-of-the-art results on CyberGym for vulnerability discovery. These are the developer's own measurements, so treat them as direction rather than proof.

On OpenRouter, GLM-5.3 takes text input and produces text output, with a context window of 1,048,576 tokens and a maximum output of 943,718 tokens. Prices are $0.079 per million input tokens and $1.40 per million output tokens. On Z.ai's own platform the model code is glm-5.3, with a 1M context and up to 128K output tokens.

Reasoning is always on for GLM-5.3. You control how much it thinks with reasoning_effort, which accepts low, high and max; the model card says it defaults to max if you do not pass a value. The open weights are on Hugging Face as zai-org/GLM-5.3, under a custom GLM-5.3 licence rather than MIT — read the licence before you build a product on the weights.

In the glm5.org chat GLM-5.3 runs with a low reasoning effort by default so answers arrive quickly. Turn on Think deeper to raise the effort when a problem deserves more care. GLM-5.3 is text only; if you attach a picture, the chat sends that message to GLM-5.3 Flash and tells you.

Because GLM-5.3 costs more to run than Flash, each visitor gets a limited number of GLM-5.3 messages per day. When the allowance runs out you can keep going with GLM-5.3 Flash in one click.