Vitamin K3

Vitamin K3 is a large language model developed by Moonshot AI, better known in the market as **Kimi K3** . It is a 2.8 trillion-parameter model built on KDA (Kimi Delta Attention) hybrid linear attention and Attention Residuals, with native vision understanding and a 1 million token context window . Moonshot AI released it in July 2026 as the world's first open-source model at the ~3 trillion parameter scale, targeting long-horizon programming, knowledge work, and reasoning .

In benchmark terms, K3 ranks just behind the top closed-source models Claude Fable 5 and GPT-5.6 Sol overall, but leads in specific domains: it topped Arena AI's Code Arena for front-end programming and scored first in front-end development, legal work, spreadsheets, creative writing, and web development in broader evaluations . At launch, it was priced at $3 per million input tokens and $15 per million output tokens—roughly 40% of Claude Opus and 20% of Claude Fable costs . Moonshot AI also open-sourced the full weights, technical report, and training infrastructure on July 27, 2026 . The model was still in training as of early 2026, with Moonshot AI's $500 million Series C round that January earmarked for accelerating K3 development .