Bun vs Rivet
Side-by-side trajectory, velocity, and editorial themes.
Bun is rewriting its core from Zig to Rust while shipping built-in APIs at a monthly clip.
Bun ships a substantial point release roughly monthly, each widening Node.js compatibility and folding more capability into the runtime itself — image processing, Markdown parsing, cron, archives, a headless WebView, HTTP/2 and HTTP/3 clients. Performance work is constant, with double-digit speedups landing release over release. In July the team disclosed it is rewriting Bun's implementation from Zig to Rust.
Two arcs run in parallel: keep absorbing what developers reach for third-party packages to do, so the runtime is batteries-included, and re-lay the foundation in Rust for a larger contributor pool and easier maintenance. The near-term feature cadence has not slowed, which suggests the rewrite is incremental rather than a hard fork.
Expect continued monthly 1.3.x releases centered on Node compatibility and built-in APIs, with the Rust migration surfaced through engineering write-ups before it changes anything user-facing.
Rivet pivots from actor backend to a coding-agent OS, and is building the ecosystem to match.
Rivet began as an actor and serverless backend platform — RivetKit, Rivet Actors, Rivet Compute — and has spent the last month reorienting around agentOS, a WebAssembly-based Linux environment for running coding agents without a heavy sandbox. The June and July releases show both threads running in parallel: native language SDKs (Rust, Effect) for Actors, and a fast-maturing agentOS that now has its own package registry.
The center of gravity is shifting from hosting stateful actors to being the runtime coding agents execute inside. agentOS went from a v0.2 sandbox alternative to shipping a package registry and a sub-millisecond package manager in under two weeks, a sign Rivet wants to own the developer surface around agent execution, not just the compute underneath it.
Expect agentOS to keep accreting ecosystem pieces — more registry content and tighter orchestration — while the Actors SDKs settle toward maintenance. A likely next move is deeper coupling between agentOS and Rivet Compute so agents run on Rivet's own cloud.
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