China's Moonshot AI releases Kimi K3, the largest open-source model ever, rivaling top U.S. systems

What happened

China's Moonshot AI released Kimi K3, a 2.8 trillion-parameter model with a 1M context window, described as the largest open-weight model in history. Weights will be open-sourced on July 27, 2026.

Context and impact

In blind Arena testing, developers preferred Kimi K3 over every leading US model for front-end coding — including Anthropic Fable 5 and GPT-5.6 Sol. The release sent shockwaves through Silicon Valley and drew alarm in Washington as China rapidly erases America's frontier AI lead.

Details

• 2.8 trillion parameters with MoE (Mixture of Experts) architecture
• Native 1M context window with Kimi Delta Attention (6.3× faster decoding)
• Pricing: ~$3/M input tokens, $15/M output tokens (comparable to Anthropic Sonnet)
• Outranks Claude Opus 4.8 in Arena leaderboard, ties with GPT-5.6 Sol
• Open-source weights planned for July 27, 2026
• Native multimodal capabilities built directly into the model