# Composer 2 Composer 2 is [[Cursor.com|Cursor]]'s coding model, shipped 19 March 2026. It replaced the original Composer (now called Composer 1), which had launched five months earlier alongside Cursor 2.0. Composer 2 was the first version Cursor was willing to call frontier-level on coding, and it held the default slot until [[Composer 2.5]] arrived two months later. ## The Composer line, briefly Composer 1's pitch was speed. It was a [[AI Mixture of Experts (MoE)|mixture-of-experts]] model tuned for software engineering, roughly 4x faster than other models of similar intelligence, with no public API because it only ran inside the Cursor IDE. Cursor trained it with reinforcement learning across hundreds of thousands of sandboxed coding environments. Composer 2 kept that speed focus and spent the new budget on getting smarter. ## What changed from Composer 1 The headline is reinforcement learning on long-horizon coding tasks, the kind that take hundreds of sequential actions before the result is correct. Cursor ran continued pretraining first to strengthen the base, then scaled the RL stage on top. The benchmark gains were not subtle: | Benchmark | Composer 1 | Composer 2 | |---|---|---| | CursorBench | 38.0 | 61.3 | | Terminal-Bench 2.0 | 40.0 | 61.7 | | [[SWE-Bench\|SWE-bench]] Multilingual | 56.9 | 73.7 | ## Foundation Composer 2 is built on [[Moonshot AI]]'s open-weight [[Kimi K2.5]] checkpoint, a detail Moonshot confirmed publicly. [[Composer 2.5]] kept the same base and pushed the post-training further still. ## Pricing (per million tokens, input / output) | Variant | Input | Output | |---|---|---| | Standard | $0.50 | $2.50 | | Fast (default, same intelligence) | $1.50 | $7.50 | On individual plans, Composer draws from its own usage pool with a generous included quota. ## Lineage Composer 1 (Oct 2025), then Composer 2 (Mar 2026), then [[Composer 2.5]] (May 2026). Every step reused the prior base model and spent most of the fresh compute on training and RL rather than a new architecture. ## References - Composer 2 announcement: https://cursor.com/blog/composer-2 - Cursor changelog: https://cursor.com/changelog - Composer 1 background (Simon Willison): https://simonwillison.net/2025/Oct/29/cursor-composer/ - Moonshot confirming the Kimi K2.5 base: https://simonwillison.net/2026/Mar/20/cursor-on-kimi/ ## Related - [[Cursor.com]] - [[Composer 2.5]] - [[Cursor CLI]] - [[Kimi K2.5]] - [[Moonshot AI]] - [[AI Mixture of Experts (MoE)]] - [[SWE-Bench]] - [[Reinforcement Learning (RL)]] - [[Large Language Models (LLMs)]] - [[AI Frontier Model]]