Copilot · GitHub · Rust · GitHub Blog
Migrating the GitHub Copilot runtime to Rust, tapping Copilot
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The GitHub Copilot CLI, GitHub Copilot app, and GitHub Copilot SDK are all backed by the Copilot agent runtime, an agentic harness that can be embedded into applications and services.
Key facts
- During the port, the runtime took in ~300,000 production lines of TypeScript and shed ~430,000, while ~1,200,000 production Rust lines entered and ~365,000 left
- The initial porting plan in early May 2026 estimated the runtime at roughly 130,000 lines of TypeScript
- Using the GitHub Copilot app and the Copilot CLI, they completely rewrote the runtime into more than 800,000 lines of production Rust
- If they look at the CLI, it’s logically a terminal UI (TUI) on top of an agent loop
Summary
That has now changed. Using the GitHub Copilot app and the Copilot CLI, they completely rewrote the runtime into more than 800,000 lines of production Rust. The Copilot agent runtime isn’t the engine behind the Copilot CLI. These are different products, and none of them wants to or should need to implement everything that goes into a production agent harness. They want all of the intelligence, security, reliability, and performance, and they want it shared so that a fix in one place fixes it in all of them. So, shared runtime, good.