Bun for AI agents: where the speed actually shows up (and where it lies)

Bun is fast. The README will tell you 4x on bun install, 3-5x on Bun.serve(), 2x on bun:sqlite. Some of this matters for AI agents. Some of it doesn't.

We've been running production agents on Bun for about 3 months — a mix of Hono-on-Bun HTTP agents and standalone Bun scripts called from Claude Code and OpenClaw. This post is what we'd tell ourselves 3 months ago about where Bun actually helps and where it bites.

Where Bun's speed actually matters for agents

Cold starts on agent scripts

Agents are spawned. A lot. Every Claude Code hook, every npx invocation, every cron-fired worker. Node's startup is ~80-120ms cold; Bun's is ~15-25ms.