Cloudflare adopts tsrs, an AI-built Rust port of the TypeScript compiler

What it's about

Cloudflare and VoidZero, the company it acquired in June, are taking over tsrs, a port of the TypeScript compiler to Rust. Cloudflare announced the move on Tuesday. A developer only started the open-source project in late September, because TypeScript used too much memory at his employer. tsrs translates Microsoft's Go implementation of TypeScript to Rust function by function. It aims to be a drop-in replacement for both the compiler and the language server (the program that gives editors error messages and autocomplete). tsrs is now also part of Oxc, VoidZero's Rust-based JavaScript toolchain.

The numbers: speed and memory

According to Cloudflare, tsrs type-checks up to eight times as fast as TypeScript 7.0 and uses about 70 percent less memory when both run with the same number of threads. The founder's own measurements against the current development version of Microsoft's Go compiler are more modest. Across 17 open-source projects, tsrs is 2.5 to 5 times as fast and needs only about a third of the memory.

The figures come from the people involved and have not been independently verified.

Why yet another Rust version?

Cloudflare points to WebAssembly (Wasm, a portable binary format that runs in browsers or sandboxed environments, for example). A Go program compiled to Wasm has to bundle its garbage collector (the automatic memory cleanup). Rust doesn't need one, so it saves memory. Cloudflare benefits directly if AI agents on its Workers platform are to run full development toolchains in sandboxed environments.

Ported by AI agents

tsrs was created by Max Schwenk, who leads AI developer tooling at restaurant software provider Owner.com. There, TypeScript 7.0 checked a backend of about 37,000 files in a single thread using 19 GB of memory and 80 seconds of runtime. That was too much to run parallel coding agents alongside it. The port was done with Anthropic's Claude Opus 5.5, and he says he wrote not a single line of code himself. According to the project documentation, tsrs matches the original on nearly all error baselines in TypeScript's conformance test suite, apart from a few artifacts attributed to the test environment. Schwenk says he handed the project to the Oxc team because he wanted to put it in the hands of people who maintain Rust tooling full time.

Microsoft's response: TypeScript 7.1

On the same day, Microsoft released the beta of TypeScript 7.1. On five codebases measured by the vendor, it needs 13 to 47 percent less time for checking than 7.0. Daniel Rosenwasser of the TypeScript team confirmed on Hacker News that part of the gain comes from optimizations taken from tsrs. His team has experimented with Rust itself, he said, and suspects that much of the speedup doesn't depend that heavily on the language.

Cloudflare rules out forking TypeScript. The language will continue to be decided solely by the TypeScript team at Microsoft. To keep the port in step, AI agents are to review the TypeScript repository daily and propose matching changes.

Availability

Cloudflare stresses the experimental nature of the current version, 0.18. The npm package is released under the Apache License 2.0 and ships native binaries for macOS on ARM processors and for Linux, but not for Windows. The goal is a stable release with full compatibility with TypeScript 7.1.

Takeaway

The case shows how quickly AI agents can port a large project that is easy to test: the existing test suite serves as the yardstick. It matters in practice for large codebases and for setups with many parallel agents, where memory is tight. Some caveats remain. The big headline gains come from Cloudflare, the more cautious ones from the founder, and Microsoft's view suggests that part of the gains comes from algorithms rather than from Rust. Also, tsrs is experimental, has no Windows binaries, and its long-term compatibility depends on automated upkeep.