Bun has released version 1.3.9 with several significant improvements for developers. The update introduces `bun run --parallel` and `bun run --sequential` commands that let you execute multiple package.json scripts concurrently or sequentially with Foreman-style prefixed output. This feature integrates fully with `--filter` and `--workspaces` for running scripts across workspace packages, making it easier to manage complex build and test workflows.

Another major addition is HTTP/2 connection upgrade support via `net.Server`, fixing a critical pattern used by libraries like http2-wrapper and crawlee. The update also brings `Symbol.dispose` support for `mock()` and `spyOn()`, enabling automatic mock restoration with the `using` keyword. This eliminates manual cleanup code and reduces test boilerplate. Additionally, Bun now respects the `NO_PROXY` environment variable even when explicit proxy options are provided to `fetch()` or `WebSocket`.

Performance improvements include SIMD-accelerated Markdown-to-HTML rendering that's 3-15% faster, faster `Bun.markdown.react()` with cached HTML tag strings reducing allocations by 40%, and optimized `AbortSignal.abort()` that skips event creation when no listeners are present. The JavaScriptCore engine upgrade brings SIMD-accelerated RegExp prefix search for significant regex performance gains. Bun also fixed crashes on older ARM64 processors and added `--cpu-prof-interval` support for CPU profiling.

Quick Fact: Bun v1.3.9 was released on February 8, 2026.