Jarred‑Sumner has rewritten Bun's core engine in Rust, a move that keeps the original architecture and data structures while eliminating memory leaks that plagued the JavaScript‑based runtime. The new code passes all existing tests on Linux, macOS, and Windows, fixing flaky behavior and cutting the binary size by 3 MB to 8 MB.

Beyond size, the Rust rewrite introduces compiler‑assisted tools that catch memory bugs at build time—a development cost that previously sapped the team hours. Benchmarks show performance that is neutral to slightly faster than the original JavaScript engine, while the project remains largely unchanged in its minimal third‑party dependencies and no async‑Rust usage.

Users can try the canary build with the command 'bun run' and report issues; the author promises further optimizations and cleanup in upcoming pull requests. The switch to Rust positions Bun as a more reliable, efficient tool for developers who rely on fast, low‑memory JavaScript runtimes.

This milestone mirrors a broader trend of rewriting performance‑critical engines in safer languages. By leveraging Rust’s ownership model, Bun eliminates a class of bugs that traditionally required extensive runtime checks. The update also opens the door for future extensions, such as native WebAssembly support, without compromising the lightweight footprint that has attracted early adopters.