What happened
Z.ai Co. released the code for GLM-5.3-Flash, an LLM with 320 billion parameters that activates 18 billion per prompt. It first appeared last week on OpenRouter Inc. as an unnamed free model called Ox Alpha, which drew industry attention.
Why it matters
The model costs ten times less to run than Z.ai's previous-generation LLM. It uses sparse attention and linear attention to cut processing power and memory, and it scored highest on the GDPval-AA v2 benchmark against Claude Opus 4.8, GPT-5.6 Terra and Gemini 3.7 Flash.
What to watch
GLM-5.3-Flash accepts up to 1 million tokens of input (text, images, video) and generates up to 131,072 tokens. Its weights are available on Hugging Face.
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Z.ai's open-sourcing of GLM-5.3-Flash follows the model's debut on OpenRouter as 'Ox Alpha' without a named developer, a move that sparked speculation and attention. The company has now confirmed its authorship and released the weights publicly on Hugging Face.
The release emphasizes cost efficiency, a key factor for businesses deploying AI at scale. The company states the model costs ten times less to run than its prior generation, achieved through architectural changes including sparse and linear attention mechanisms that reduce processing and memory demands.
Benchmark results place GLM-5.3-Flash competitively, with the highest score on GDPval-AA v2 against Claude Opus 4.8, GPT-5.6 Terra, and Gemini 3.7 Flash, and second place on AutomationBench. Training used a 30 trillion token dataset and a technology called mHC to reduce gradient distortion.
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