Inside the Composer 2 training pipeline

Everything in the prior sections is theory until you see it wired into a real run. Composer 2Cursor's own coding model, built on the open Kimi K2.5 base as a software-engineering specialist. Cursor calls it frontier-level at coding and more cost-efficient than comparable models; Composer 2.5 has since replaced it in Cursor's model list. Press Enter for the full definition. is that run: long-horizon RLlong-horizon reinforcement learning. Reinforcement learning on realistic coding tasks that take many steps: the model makes a group of attempts at each problem and is updated toward the better solutions. Cursor says Composer 2 can solve tasks that need hundreds of actions, and its Composer 2.5 post says rollouts can span hundreds of thousands of tokens. Press Enter for the full definition. on real coding problems, in simulated copies of real repos, scored on real test outcomes.

Cursor has described the pipeline in enough detail that you can reason about each stage. Treat this section as a worked example the deep-dive may circle back to: where do the problems come from, how does an environment get built, and how do you train past the context window when a single rollout runs huge.