Bun Rust Rewrite Branch Sparks Debate

The interesting part isn’t “Bun is rewriting itself in Rust”; it’s that the team is turning a language migration into a measurable, test-driven experiment rather than a vibes-only rewrite.

• –Reports from the branch suggest it reached 99.8% test compatibility on Linux x64 glibc after starting from thousands of compiler errors, which makes this a serious porting exercise rather than a toy fork.
• –The porting guide matters as much as the code: translating Zig idioms into Rust gives other systems teams a concrete template for AI-assisted migration work.
• –The discussion is really about tradeoffs: Rust may improve safety and maintainability, but Bun’s current Zig-first identity is part of its performance and engineering story.
• –Because this is still a branch, the main signal is process, not product commitment; the real question is whether the experiment reveals enough upside to justify a future rewrite.