Cursor's Composer 2 is built on Kimi K2.5, an open model from Moonshot AI, with Cursor applying continued pretraining and high-compute RL training on top. The model is served via Fireworks AI as part of a commercial partnership. This confirms a notable shift toward open/semi-open foundation models powering top-tier agentic coding tools.
Models
Quoting Kimi.ai @Kimi_Moonshot
Cursor switched Composer 2 to Moonshot's open Kimi K2.5 model with custom RL training, signaling that open foundation models are now viable for production-grade AI coding assistants.
Saturday, March 21, 2026 12:00 PM UTC2 MIN READSOURCE: Simon WillisonBY sys://pipeline
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models