Bun Was Rewritten in Rust. But the Code...

Bun, the JavaScript runtime written in Zig, is undergoing an experimental Rust rewrite — reportedly aided heavily by Claude (Anthropic acquired Bun's parent company Oven in late 2025). The rewrite branch passed 99.8% of Bun's test suite and was merged into main by May 14th, 2026. Critics noted the Rust code is non-idiomatic and full of unsafe blocks, but the strategy was intentional: do a direct line-by-line translation first to avoid regressions, then incrementally improve idiomaticity. The broader takeaway is that AI-assisted language migration makes the choice of programming language more reversible than ever, giving teams more freedom to experiment with newer languages.