Cursor's Composer 2 is built on Kimi k2.5 base model with added training

Aman Sanger says Cursor's team evaluated many base models on perplexity-based evals and found Kimi k2.5 the strongest. Composer 2 was then built with continued pretraining and a 4x scale-up of high-compute RL, with Fireworks providing inference and RL samplers. The author admits Cursor should have named the Kimi base in its launch blog and says it will do so for the next model.