Bun rewrote itself from Zig to Rust using an LLM in 9 days. That should terrify you.

A major runtime just got machine-translated to a completely different language and merged in under two weeks. Let me say that again slowly.

Bun, the JavaScript runtime that the community keeps considering for a serious relationship, finished a rewrite of itself, from Zig to Rust. The rewrite was composed in its majority by the LLM model. The process lasted around 9 days. The Pull Request contained over 1M LoC of Rust.

I don't think everyone realizes how amazing that is.

This Isn't a Rewrite. It's a Translation.

Rewriting software and translating software are worlds apart. The former involves humans re-thinking the architecture, fixing old mistakes, and inevitably making some new and different mistakes in the new language. A translation means you shove code through a machine and hope the output is equivalent.