Bun Has Been Converted to Rust. Now What?
Bun has transitioned from a Zig implementation to Rust, with over a million lines of code rewritten in just nine days. The motivation for this change was to enhance memory safety, although the new code contains over ten thousand unsafe blocks. While the rewrite passed 99.8% of the existing test suite, concerns remain about the actual safety and quality of the new implementation.
- ▪The Rust rewrite of Bun was completed with 6,755 commits and involved a million lines of code.
- ▪Despite the transition aiming for memory safety, the new implementation has over ten thousand unsafe blocks.
- ▪The rewrite passed 99.8% of the existing test suite, indicating behavioral equivalence with the old implementation.
Opening excerpt (first ~120 words) tap to expand
Bun Has Been Converted to Rust. Now What?By dreamreal|June 3, 2026|Updated 12:14pm ETaibunmemoryrustOn May 14, PR #30412 merged into Bun's main branch: a little over a million lines of Rust, 6,755 commits, generated almost entirely by Claude Code agents over nine days. Anthropic, which acquired Bun in December, supplied the agents. The Zig implementation that powered Bun is gone. Jarred Sumner's own words - "we haven't been typing code ourselves for many months now" - are the part everyone quoted, and the part that turned a routine merge into a 685-point Hacker News thread with the PR itself split almost evenly between thumbs-up and thumbs-down. The Rust rewrite passed 99.8% of the existing test suite.
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