How to port a runtime to Rust with Copilot

The supplied article describes Microsoft using Copilot to rewrite the runtime underpinning Copilot products from TypeScript into Rust. The migration proceeded module by module, replacing individual TypeScript components rather than restructuring the entire runtime. Structural optimization was described as future work.

Agents used multiple models, including GPT-5.6 Sol and Claude Opus 4.8, for different parts of the task. The article describes an investigative pattern: inspect the current state, form a hypothesis, make a targeted change, and repeat. One difficult session.ts conversion involved a file exceeding 30,000 lines that touched many runtime components.

That session began with documentation reading and clarification tool calls, then spawned 15 child sessions with separate worktrees and agents. A built-in orchestration skill helped a session locate other active sessions and request coordination where their assignments overlapped.

The article reports a completed conversion of 430,000 TypeScript lines into 800,000 production Rust lines across more than 135 releases. It also reports roughly $120,000 in token usage, about three weeks of developer time, and a few dozen regressions. Reported speed and memory improvements refer to particular benchmark workloads, rather than every runtime operation.

Who it's for: teams evaluating agent-assisted language migrations with substantial cross-module coordination requirements.

Prompt
Suggested prompt (written by Agents In Use, not the author's)

Source: Blog · pjmlp