A technical report on Composer 2

Details the training of Composer 2, a coding model for agentic software engineering. This includes continued pretraining on Kimi K2.5, large-scale reinforcement learning emulating the real Cursor environment, and evaluation using CursorBench. The post highlights performance improvements over Composer 1.5 and competitive results on public benchmarks, achieved at lower inference cost. It also describes the underlying infrastructure, including custom low-precision kernels for MoE training on Blackwell GPUs, an asynchronous RL pipeline, and Anyrun for running sandboxed coding environments.