Cursor’s engineering team has shared technical details and challenges from building Composer and shipping their coding agent into production. This article breaks down those engineering challenges and how they solved them.

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Cursor's Composer is an agentic coding system that combines a specialized MoE language model with tool harness, context retrieval, and sandboxed execution. The engineering challenges included solving the "diff problem" where models struggle with precise code edits, managing compounded latency through MoE architecture, speculative decoding, and context compaction, and building custom sandboxing infrastructure to handle thousands of concurrent isolated execution environments. The system routes requests between models, iterates through a ReAct-style loop using tools like search and file editing, and verifies changes by running builds and tests in secure sandboxes.

How Cursor Shipped its Coding Agent to Production

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