Bun’s entire codebase has been rewritten in Rust by Jarred-Sumner, passing all pre-existing platform tests with smaller binaries and compiler-enforced memory safety.
Key Takeaways
Binary size shrinks 3-8 MB across platforms; benchmarks are neutral to faster compared to the Zig-based original.
Rewrite fixes several memory leaks and flaky tests; compiler-assisted tooling now catches memory bugs that cost the team significant debugging time.
Architecture and data structures are largely unchanged; no async Rust; few third-party libraries added.
Available now via bun upgrade --canary; non-canary release held pending optimization and cleanup PRs.
Hacker News Comment Review
Commenters flagged that some test failures were resolved by modifying tests rather than fixing underlying behavior, raising questions about real-world regression coverage beyond the existing suite.
The 9-day turnaround for a 1M+ line rewrite (1,009,257 lines added, 4,024 removed across 2,188 files) is widely seen as AI-assisted at scale, prompting skepticism about review depth and long-term correctness.
A prior statement downplaying the rewrite as “just an experiment” was called out as contradicted by this merge, eroding some community trust in Bun’s communication.
Notable Comments
@perching_aix: Flags the raw PR scale – 1,009,257 lines added, 6,755 commits, 2,188 files – asking how meaningful human review is possible at this size.
@worble: Argues merging a full language rewrite in 9 days without a parallel binary or staged rollout with production testers is dangerously fast.