Cloudflare and VoidZero back tsrs, a Rust port of TypeScript, and plan to merge it with tsc-rs

Cloudflare has introduced tsrs, a Rust port of the TypeScript compiler’s type checker. Cloudflare and VoidZero are building it with Max Schwenk of Owner.com, “in close collaboration with the TypeScript team”, and it is being incubated in the Oxc JavaScript toolchain. The repository is Apache-2.0 and was created on 1 October.

“To be clear, we are not forking TypeScript,” the post says. The TypeScript team keeps control of the language, and tsrs has to follow its decisions to stay compatible.

The numbers, and their context

Cloudflare’s early benchmarks say tsrs is up to 8x faster and uses about 70% less memory than TypeScript 7.0 with the same number of type-check workers. The post adds that it worked with the TypeScript team so both sides ran the same configuration, and that the TypeScript 7.1 beta is itself up to 2.5x faster than 7.0, partly from optimizations upstreamed from tsrs. By default tsrs picks a machine-dependent configuration that uses more memory to go faster still. These are Cloudflare’s measurements, not an independent test.

You can try it with npm install tsrs. The current npm release is 0.18.0-ts7.1.0-dev.20260929, published on 19 October, and Cloudflare notes there are still differences from upstream, such as the order diagnostics are printed in.

Where AI comes in

Two places. First, Cloudflare credits frontier models with making the port feasible at all: they “can now do large-scale ports almost independently in a matter of days”, and the post mentions “slopforks, faithful ports, and completely re-architected versions” already in the wild. The post does not say how much of tsrs itself was written by AI.

Second, maintenance. Cloudflare says it is working with Theo Browne to merge tsc-rs, the Rust port we covered earlier this month, and tsrs into one package with language-server support. It also plans to keep tsrs in step with TypeScript using the same process it uses for Vinext and Next.js: an agent reviews upstream changes each morning and opens tracking issues, the test suite runs nightly, and agents build reproductions and propose fixes. The merge is announced intent; the tsc-rs repository is still separate today.

Why Rust

The pitch is WebAssembly. A Go program compiled to Wasm carries Go’s garbage collector with it, and Cloudflare argues Rust’s memory model makes a smaller, cheaper Wasm build. That matters for running whole dev toolchains in Workers sandboxes, in browsers or on small devices, which is the case tsc-rs 0.7 was also chasing.