Kimi K3 Fast is the Fireworks AI router-hosted variant of Moonshot AI's Kimi K3, an open-weight model introduced in mid-2026 as a 2.8-trillion-parameter system built around a new mixture-of-experts design that combines Kimi Delta Attention with Attention Residuals and activates 16 of 896 experts under a Stable LatentMoE framework. The "Fast" deployment preserves the underlying K3 capabilities while exposing them through a hosted inference endpoint, giving teams access to the same architecture without managing weights themselves. The Hugging Face mirror maintained alongside Moonshot's official release ties the router listing directly to Moonshot's Kimi K3 model card, tech report, and research blog, confirming shared lineage.
Positioned by Moonshot as the world's first open 3T-class model, Kimi K3 Fast targets long-horizon coding, knowledge work, and advanced reasoning, with a one-million-token context window that supports extended document analysis and multi-step agentic workflows. Independent coverage highlighted a benchmark win in the Frontend Code Arena against Anthropic's Claude Fable 5, and the model carries native vision capabilities so it can ingest images alongside text. Through the Fireworks router, multimodal inputs, tool calling, structured output, and reasoning traces are available as standard capabilities, making the model a fit for production assistants that need frontier-class open-weight intelligence, agentic tool use, and very large context for code or research tasks.
