A surprising headline (with caveats) Last week a tweet from Jarred Sumner — Bun's creator — made the rounds claiming a Zig-to-Rust rewrite is passing 99.8% of the testsuite. I haven't been able to independently verify this through Bun's official release notes or the changelog at bun.sh , so take the specifics with a grain of salt. According to early reports it's a real effort, but I'd treat the exact percentage as anecdotal until something hits the official channels. The conversation it kicked up on Reddit and HN is still worth digging into. It surfaces a question I've been chewing on for years: when does it actually make sense to rewrite a working systems project in a different language? I've migrated three production services between languages over the last few years (Go to Rust twice, Node to Bun once), so let me walk through what a Bun rewrite would mean — and use it as a lens for the broader Zig vs Rust comparison. Why anyone rewrites in the first place Rewrites are almost always a bad idea.…