Vercel Functions now support the new Bun 1.4 release, a rewrite of Bun from Zig to Rust, with over 2,900 issues resolved, more than 1,500 additional Node.js compatibility tests passing, and new features and performance improvements.

Bun on Vercel Functions:

• Runs on Fluid compute with Active CPU pricing

• Supports WebSockets and Bun.serve()

• Supports common frameworks such as Next.js, Elysia, and Hono

To update from the previous Bun version, set bunVersion to 1.4.x in vercel.json.

Upgrading is an explicit opt-in because Bun 1.4 has several breaking changes. Review the breaking changes and update your application before upgrading.

Learn more about using Bun on Vercel in the runtime documentation.