Simon Willison’s Weblog

GLM-5.2 is probably the most powerful text-only open weights LLM

17th June 2026

Chinese AI lab Z.ai released GLM-5.2 to their coding plan subscribers on June 13th, and then yesterday (June 16th) released the full open weights under an MIT license. Similar in size to their previous GLM-5 and GLM-5.1 releases, this is 753B parameter, 1.51TB monster—with 40 active parameters (Mixture of Experts). GLM-5.2 is a text input only model—Z.ai have a separate vision family most recently represented by GLM-5V-Turbo, but that one isn’t open weights. GLM-5.2 has a 1 million token context window, up from GLM-5.1’s 200,000.

The buzz around this model is strong.

Artificial Analysis, who run one of the most widely respected independent benchmarks: GLM-5.2 is the new leading open weights model on the Artificial Analysis Intelligence Index.

GLM-5.2 is the leading open weights model on the Intelligence Index v4.1. At 51, it leads MiniMax-M3 (44), DeepSeek V4 Pro (max, 44) and Kimi K2.6 (43)

They did however find it to be quite token-hungry:

GLM-5.2 uses more output tokens per task than other leading open weights models: the model uses 43k output tokens per Intelligence Index task, up from GLM-5.1 (26k) and above MiniMax-M3 (24k), Kimi K2.6 (35k) and DeepSeek V4 Pro (max, 37k)

The model is also now ranked 2nd on the Code Arena WebDev leaderboard, behind only Claude Fable 5. That leaderboard measures “front-end web development tasks, including agentic coding workflows”. I’m impressed to see it rank so highly given the lack of image input, which I had incorrectly assumed was a key part of building a truly great frontend coding model.

I’ve been trying it out via OpenRouter, which has it from 9 different providers, almost all of which are charging $1.40/million for input and $4.40/million for output. For comparison, GPT-5.5 is $5/$30 and Claude Opus 4.5-4.8 is $5/$25.

Excellent pelican, disappointing opossum

GLM-5.1 gave me one of my favorite pelicans and my all time favorite opossum (for the prompt “Generate an SVG of a NORTH VIRGINIA OPOSSUM ON AN E-SCOOTER”.) Interestingly, in both of those cases the model chose to return SVG wrapped in an HTML document that added additional animations using CSS.

Let’s try GLM-5.2. For “Generate an SVG of a pelican riding a bicycle” I got this:

It’s a self-contained fully animated SVG, and the animations aren’t broken! Often I’ll see eyes falling off or wheels rotating independently of the bicycle but here everything works great. It’s a very nice vector illustration of a pelican too. Very impressive.

Sadly, the NORTH VIRGINIA OPOSSUM ON AN E-SCOOTER did not come out nearly as well:

This is such a step down from GLM-5.1! As a reminder, that possum looked like this:

5.2 didn’t even try to animate it.