Kimi K2 is Moonshot AI’s original K2-generation base model, released in July 2025 as one of the largest open-weight language models available at the time. It uses a mixture-of-experts design with about 1 trillion total parameters and 32 billion active per token, and it supports a 128,000-token context window. Moonshot built it around agentic use cases such as tool calling and multi-step task execution rather than pure chat, and on coding benchmarks like the multilingual HumanEval variant MultiPL-E it scored close to the best closed models available that summer. The weights are released under a modified MIT license, so companies can download, fine-tune, and self-host it instead of going through Moonshot’s API, and it became the base that later Moonshot releases, including K2.5, K2.6, and K2.7 Code, built on top of.