Bun 1.4 rewrites the runtime in Rust and adds 1,517 passing Node.js tests
Bun 1.4 rewrites the runtime from Zig to Rust and adds 1,517 Node.js test-suite tests, with node:http, node:fs, and node:stream passing 97% of Node's own suite. The drop-in claim is closer to literal — Playwright, vitest, and Next.js 16 run under Bun now — and long-running apps get 5x lower idle CPU, up to 35% less memory on HTTP servers, and 50% faster startup on Linux.
Source: bun.com ↗
For Claude Code, a large long-running application built on Bun, production CPU usage dropped by 2×: p99 from 24% to 10%, p50 from 5.8% to 2.5%.
Bun team
Why this matters
- → 97% Node.js test compatibility eliminates major switching cost
- → 5x lower idle CPU and 35% less memory make Bun viable for production servers
- → Rust rewrite improves performance and stability for long-running apps
From Zig to production-ready