It took nine days to rewrite all of Bun from Zig to Rust using an LLM and get the new code to the point where I could merge it. I saw that and my reaction was not “cool.” It was “oh no.”
Let me be clear. The speed isn't what scares me. The confidence is.
Why This Hits Different
Bun's lead developer had publicly downplayed the idea of a Rust rewrite just days before it happened. Then an LLM-assisted rewrite landed and got merged in nine days flat.
This is not just refactoring some part of the codebase. It's not porting a utility library. It's literally re-implementing an entire JavaScript runtime system - which is known to be one of the most complicated pieces of software.
