Why Bun is faster than Node
Bun is written in Zig, a low-level systems language that compiles to native code. Node.js is written in C++ and JavaScript with V8 engine. The architectural difference: Bun is a single binary with the JavaScriptCore engine (from WebKit), no separate node_modules, no separate runtime. The result: startup is 4x faster, package installation is 3x faster, test execution is 3-4x faster. For saas.pet, my build times went from 45 seconds (Node) to 18 seconds (Bun). The trade-off: Bun uses more memory at startup (40MB vs Node's 25MB) but is more memory-efficient under load.
Real benchmarks from saas.pet
I ran the same workflow (install dependencies, run tests, build site, run dev server) on both Node and Bun. Install dependencies: 18s (Bun) vs 47s (Node). Run all tests: 4s (Bun) vs 18s (Node). Build production site: 18s (Bun) vs 45s (Node). Start dev server: 0.3s (Bun) vs 1.8s (Node). Total time saved per CI run: ~90 seconds. The dev server cold start is the biggest productivity win: no more waiting 2 seconds for the server to be ready. The benchmark results match the published numbers from the Bun team, with saas.pet benefiting from the fast file system operations (Bun has a native SQLite client and fast fs.readFile).
The compatibility story
Bun claims Node.js compatibility, and it is about 95% there. For saas.pet, the things that work: npm packages (all of saas.pet's 15 dependencies installed cleanly), TypeScript (built-in, no need for ts-node), package.json scripts (no changes needed), fetch API (Node 18+ compatible). The things that do not work: some native modules (better-sqlite3 needs a rebuild), a few obscure npm packages (less than 1% of the registry), and some edge cases in test frameworks. The Bun team actively works on Node compatibility, so the gap closes every release. For a project starting fresh, Bun is a no-brainer. For a project migrating from Node, expect 1-2 days of fixing compatibility issues.
The production deployment gotchas
Vercel still uses Node for serverless functions. You cannot deploy Bun to Vercel as the runtime. For production, saas.pet still uses Node. Bun is excellent for local development and build pipelines, but production is still Node. There are workarounds (Bun runtimes on Cloudflare Workers, Railway, Fly.io) but they are not yet mainstream. If you need to deploy to Vercel, you are still using Node. For self-hosted deployments, Bun is production-ready. The Bun team has discussed adding Vercel support but no timeline. Until then, Bun is a developer tool, not a deployment target.
Who should use Bun
Use Bun if: you are starting a new project, you do heavy TypeScript development, you run a lot of test scripts, or you want faster CI pipelines. Skip if: you are locked into Node-specific libraries (e.g., native modules without Bun support), you need maximum library compatibility, or you deploy to platforms that require Node. The 94K stars and active development (2-3 releases per month) mean Bun is maturing fast. For saas.pet, I use Bun for local development and the build pipeline, and Node for the Vercel production deployment. The combo gives me the best of both worlds. For most developers starting new projects in 2026, Bun is the right choice.
