China’s Kimi K3 Becomes Largest Open-Weight AI Model Ever
2 min readChina just raised the stakes in open-source AI. Moonshot AI has published the open weights for Kimi K3, a 2.8-trillion-parameter model that is now the largest open-weight system ever released to the public. The files went live on Hugging Face on July 26, roughly a day ahead of the company’s own July 27 target, free for anyone to download.
What was released
Kimi K3 is a frontier-class model with native vision and a context window of up to one million tokens. The full weights weigh in at about 1.4 terabytes using MXFP4 quantization. Under the hood, Moonshot pairs its Kimi Delta Attention design with a highly sparse mixture-of-experts system that activates just 16 of 896 experts for any given inference, keeping running costs manageable despite the enormous parameter count.
How it stacks up
In blind developer testing on the LMArena Frontend Code evaluation, Kimi K3 ranked first with 1,679 points, edging out Anthropic’s Claude Fable 5. Moonshot is candid that on overall performance the model still trails Fable 5 and OpenAI’s GPT-5.6 Sol, but it topped every other system in the company’s own coding and agentic benchmark suite.
The bigger point is access. Where the leading American models are locked behind paid APIs, a model in the three-trillion-parameter class is now downloadable at no cost, letting researchers and startups run and fine-tune it on their own hardware.
Why it matters
The release lands as the United States continues to restrict China’s access to the most advanced AI chips. By shipping the largest open model in the world, Moonshot is signaling that Chinese labs can compete at the frontier despite those compute limits, and it hands the global open-source community a tool that rivals closed systems from the biggest Western labs.
Expect a wave of hosted versions, fine-tunes, and fresh benchmarks in the coming weeks as developers put Kimi K3 through its paces. For a field increasingly split between open and closed camps, this is a decisive move for the open side.