Bun was originally written in Zig. It was one of the Zig language’s flagship projects that was brought up everywhere as an example of a successful Zig project, alongside Tiger Beetle and Ghostty.

The Bun team did an experiment to have an LLM transliterate the codebase to Rust and then iterate on turning it into idiomatic Rust. They were losing a lot of time dealing with memory management problems and wanted to move to a language with more memory safety built in rather than Zig’s very manual cleanup, which is challenging in a project like Bun that is dealing with running another language.

The Bun team posted a small blog post about the migration with technical details about how they’re doing it, along with some thanks to the Zig team and positive notes about Zig. The Zig language creator posted a blog post where he ranted about the Bun creator writing “slop before LLMs” and being a “stinky manager” according to “juicy grapes” he heard through the grapevine and numerous other attacks. It was an emotionally charged response to one of the language’s flagship projects leaving for another language.

This split the community, or at least became divisive for a lot of people who have no interest in Bun but view the fight as a proxy for some other battle like hating LLMs or Rust.

It didn’t actually kill the project. The team was acquired by Anthropic and it (the Rust version) is being used in their products, so it’s actually running everywhere and doing more than ever. There was a poll on some subreddit that showed only 30% of people were going to keep using it after the rewrite and people keep holding this up as evidence that the project is dead.