Jarred Sumner, creator of Bun — the JavaScript runtime that Anthropic bought, that just got rewritten from Zig to Rust, and that Claude Code happens to run on, so it’s a safe bet you already have it on your machine — wrote a post about why they moved to Rust. https://bun.com/blog/bun-in-rust
Short version: the runtime got 10% smaller, starts 10% faster, and “seems” to have no memory leaks, even though the codebase now has 13,000 unsafe calls in it. Jarred is happy regardless, and says he rewrote the whole thing in 11 days with early access to the Fable model — that is, with a pile of free tokens. Tokenmaxxing, senior-engineer style. He points out the original runtime took a year to write, barely leaving the house, so delegating a rewrite like this to AI is a genuine win. Great post. Everyone should write one of these after a big migration. But then —
Andrew Kelley, creator of Zig, replied. And Andrew’s post is a masterclass — a masterclass in how to thank someone, say goodbye, and toxically knife them, Linus-style, all in the same paragraph. Andrew writes that Jarred used to work closely with the Zig team — of course he did, a big successful project on a young language is fantastic advertising for that language. Jarred donated $60k a year to keep Zig funded. But then Jarred became a manager (brutal). Andrew says Jarred sold out (he did, a little), wishes Bun well while taking a jab that the Rust-rewrite post reads like it was written by marketing (still knifing), and notes Jarred went mainstream — got a job — and betrayed “our philosophical life.” https://andrewkelley.me/post/my-thoughts-bun-rust-rewrite.html
While the language creator and the creator of the flagship project built on it work through the end of the honeymoon phase and a bit of a midlife crisis — Andrew should probably take up pickleball, Jarred should go run a marathon — it’s worth sitting with the actual claim: that rewriting a runtime from one language to another is now “easy.” Twitter’s back-of-envelope crowd priced the rewrite at $165,000, which isn’t much at all. And it’s not like this is the first time — Postgres has a Rust port, SQLite has one, there’s a pile of these projects now. Yet Rust is still, somehow, a niche language with a devoted following. Open source still finds it a hard sell. Big Tech, meanwhile, eats it up — because fights exactly like this one happen inside big companies every single day. They just don’t end up on Twitter.