Union Alpha arrives in Codex: 300-400 tok/s, 262k context, free for a week

Ziwen @ziwenxu_Originally posted 2026.09.17

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Union Alpha is now in Codex!! The speed is insane over 300 to 400 tokens a second, 262k context, images in, and it's free for a week. It's a good timing too, most of the Codex usage is basically gone right now. Zai did this exact thing in August: Ox Alpha showed up unnamed, free for a week, built for agentic coding, and a week later it was GLM-5.3-Flash. So what model do you guys think it is?

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