Bun on Vercel

Vercel supports Bun as a runtime. To enable it, add "bunVersion": "1.x" to your vercel.json:

{
  "bunVersion": "1.x"
}

That's it. Vercel will use Bun instead of Node.js to run your project.

This works with any framework — backend apps (Express, Hono, Elysia), frontend frameworks, or anything else. Bun is used as the runtime, so Bun-specific APIs and features are available.

Example: Elysia with Bun

Elysia is a Bun-native framework. To use it on Vercel:

vercel.json:

{
  "bunVersion": "1.x"
}

package.json:

{
  "type": "module",
  "dependencies": {
    "elysia": "^1.0.0"
  }
}

server.ts:

import { Elysia } from 'elysia';

const app = new Elysia().get('/', () => 'Hello Elysia!');

export default app;

Example: Next.js with Bun

vercel.json:

{
  "bunVersion": "1.x"
}

package.json:

{
  "scripts": {
    "dev": "bun run --bun next dev",
    "build": "bun run --bun next build"
  }
}

Anti-Patterns

• Forgetting bunVersion in vercel.json: Without it, your project runs on Node.js. Bun-specific APIs (like Bun.file()) will fail at runtime.