There were thirteen thousand unsafe blocks. This text was generated by AI. It was sent to a JavaScript runtime that millions of developers use. Take a moment to think about that.
Bun's massive Rust rewrite and its experimental multithreading PR have both landed recently, and the discourse around them has been… something. The headline achievements are real: Bun rewrote its core in Rust and is experimenting with true multithreading. But the way it got there should make every engineer uncomfortable.
What Actually Happened
The majority of the Rust rewrite was written by Claude AI. This is not gossip – it has been openly stated by the Bun team. The rewrite added more than 13,000 unsafe blocks to the codebase. And it was released without a concurrent garbage collector.
For the non-systems folks: "unsafe" in this context means code that bypasses memory safety guarantees. One unsafe block may not be problematic. Thirteen thousand of them in AI-generated code is a different conversation entirely.
