“We are not forking TypeScript”: Cloudflare spearheads Rust port written by agents, for agents

Cloudflare has taken ownership of tsrs, a Rust port of TypeScript that the company says is up to eight times faster and uses 70% less memory than TypeScript 7.0. The pitch is simple: if AI agents are going to write and validate code in tight loops, the compiler can’t be the thing that runs out of steam first. But Cloudflare is also careful to draw a line. This is not, it insists, a fork of TypeScript.

That distinction matters because the company wants Microsoft to keep steering the language. In the blog post announcing the move, Cloudflare engineers Christoph Nakazawa, Boshen Chen and Dimitri Mitropoulos say TypeScript’s design and direction should remain in Microsoft’s hands. Nakazawa also says the work is already feeding back into Microsoft’s own compiler: TypeScript 7.1 is reportedly about 2.5 times faster as a result of shared optimizations.

There’s a practical reason Rust is attractive here. TypeScript, originally released by Microsoft in 2012, checks types before code runs, but those checks can get expensive in large projects. Microsoft already shipped a major rewrite in July with TypeScript 7.0, moving the compiler from JavaScript to Go and claiming roughly tenfold speed improvements. Cloudflare points out that Rust has tighter memory control and works well with WebAssembly, which matters if development tools are going to live inside browsers and isolated Workers sandboxes.

The project started last month at Owner.com, where head of AI developer experience Max Schwenk was staring down a 37,000-file TypeScript backend. He says Microsoft’s Go compiler used 19 GiB of memory and took 80 seconds for a single-threaded check, which made concurrent coding agents hard to use. Schwenk says he let Anthropic’s Claude Opus 5.5 and more than 20 AI subagents do the rewrite, while he handled direction and evaluation. By the next morning, he had a working typechecker.

Since then, the numbers have improved further: Schwenk says typechecking is down to about seven seconds in CI, and across more than a dozen public projects, tsrs has run 2.5 to five times faster than Microsoft’s newer Go compiler nightly while using about a third as much memory. The catch is obvious. A compiler that is fast but wrong is just a very efficient way to ship bugs, so Cloudflare is leaning on conformance tests, real-project error injection and Miri checks to keep behavior aligned with upstream TypeScript. Even now, differences remain, including diagnostic ordering. The company says it will keep watching for drift.

And the bigger story here is not just performance. It’s that the AI-agent era is pushing compiler and tooling teams toward whatever system can be checked, rebuilt and compared fastest. Rust keeps showing up as the preferred answer when memory and parallelism start to matter more than nostalgia.