Well they haven't lost anything yet. Somebody is vibe coding a rewrite in another language and we don't know much else. The author said he will write a blog post about it soon. So far all we know is it is passing most of the test suite.

But Bun has open issues and bugs. The test suite doesn't tell us whether it has introduced many new bugs, solved existing ones the test suite doesn't catch, or anything else. Not to mention, the rewrite is 960K lines that nobody understands. How long will it take for the Rust version to be better, and be understood as well as its current maintainers understand the Zig version?

Having a project consider a rewrite isn't so big a deal. Zig has been designed from the ground up with a vision, and isn't worried about taking a while to create a stable API to achieve that vision. The self-hosted backend shows how incredibly fast incremental compilation is when the language is built for it ground-up. Compared to other languages that implement weaker forms of incremental compilation it isn't even close.

I don't think the Zig team is concerned at all.