bun vercel-functions websockets deployment runtime

Bun.serve now deploys directly on Vercel Functions

Drop `Bun.serve()` into Vercel Functions without framework wrapping; WebSocket support routes to Fluid compute with per-message billing.

Summary

Eliminates the adapter layer between local Bun development and Vercel deployment—what you test locally deploys unchanged. WebSocket pricing shifts from connection time to CPU time, making real-time apps cheaper to operate at scale.

Why it matters

Implementation verdict

Replaces framework-based function wrappers for Bun projects. Requires setting `"bunVersion": "1.x"` in `vercel.json` and restructuring entrypoints to use `Bun.serve()`. Ready now for new projects; existing Vercel function code needs migration. Worth trying if you're already in the Bun ecosystem.

Sources

1.The Bun runtime for Vercel Functions now supports Bun.serve() as a function entrypoint, including WebSocket handlers.
2.The server you run locally with Bun deploys as-is, without being wrapped in a framework.
3.WebSocket connections run on Fluid compute with Active CPU pricing, so you pay only for time spent processing messages, not idle connection time.
4.Enable the runtime by setting "bunVersion": "1.x" in vercel.json.

Dev Signal

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