Rewriting Bun in Rust
Jarred Sumner completed a full rewrite of Bun from Zig to Rust, promising significant performance improvements and sharing deep technical insights.
- Bun’s core engine has been fully rewritten from Zig to Rust, aiming for performance and safety improvements.
- The migration process included dynamic workflows, trial runs, and adversarial code review to ensure robustness.
- Rust’s memory safety and concurrency features were key drivers behind the language switch.
- The rewrite reflects a growing industry trend toward safer, more maintainable systems programming languages.
Jarred Sumner, creator of the Bun JavaScript runtime, has completed a major rewrite of the project’s core engine, transitioning from Zig to Rust. The rewrite, teased since May 2025, delivers tangible performance gains while introducing sophisticated engineering practices such as dynamic workflows, trial runs, and adversarial code review. Sumner’s detailed blog post outlines the technical challenges and solutions behind the migration, highlighting Rust’s memory safety and concurrency advantages over Zig.
The rewrite represents more than a language change; it reflects a broader trend in JavaScript runtime development, where performance and reliability are increasingly prioritized. Bun’s shift to Rust also aligns with industry moves toward safer, more maintainable systems programming languages. The project’s transparency in documenting the process provides valuable insights for developers considering similar migrations.
Source: Rewriting Bun in Rust. Read the full piece at the source.
Developers working with JavaScript runtimes or considering language migrations will gain actionable insights from Bun’s rewrite process.
Highlights the practical benefits of Rust in performance-critical systems.
- Bun
- A modern JavaScript runtime designed for speed and compatibility.
- Zig
- A systems programming language focused on performance and safety.
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