Moonshot AI Releases Kimi K3, the Largest Open-Weight AI Model at 2.8T Parameters

Beijing-based Moonshot AI, backed by Alibaba, released the full weights of its Kimi K3 model on Hugging Face on July 27, 2025, making it the largest open-weight AI model ever published at 2.8 trillion parameters. K3 uses a mixture-of-experts architecture that activates only a fraction of its parameters per token, making it feasible to run despite its massive size. The model tops independent frontend coding benchmarks, outperforming closed flagship models from Anthropic and OpenAI, and supports a context window of over one million tokens with flat pricing at $15 per million output tokens. However, independent testing by developer Simon Willison revealed that K3's reasoning-heavy token usage can drive up real-world costs significantly, with one simple task consuming over 13,000 reasoning tokens before producing any output. This gap between benchmark performance and practical cost efficiency raises questions about how well the model's marketing aligns with actual deployment economics.