Simon Willison: Kimi K3 and Its License — Open Weight Is Not Open Source

Main idea

Moonshot AI released Kimi K3 weights (2.8 trillion parameters, 1.56 TB) on Hugging Face on July 27, 2026. Simon Willison points out that Moonshot deliberately avoids the word 'open source' — the model is 'open weight,' which is an important terminological and licensing distinction.

Context

Willison wrote at a time when Kimi K3 was the focal point of a geopolitical dispute: the White House accused Kimi K3 of distilling Anthropic Fable 5, China responded with countermeasures. It was also the largest open-weight release in history.

Why it matters

Kimi K3's license sets a precedent: Model-as-a-Service companies earning over $20M/year must negotiate separately with Moonshot. This effectively separates community use (free) from commercial use (paid) — similar to some open-source licenses but more explicit.

Details / arguments

• Kimi K3 weights: 1.56 TB on Hugging Face (MXFP4 quantization)
• Moonshot consistently uses 'open weight,' not 'open source'
• License requires attribution for entities above certain thresholds
• MaaS businesses earning over $20M/year must sign a separate agreement with Moonshot
• Sets precedent for future Chinese open-weight releases and their licensing terms