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Bun 1.4 is now available in Vercel Functions
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Vercel Functions now support Bun 1.4, a Rust rewrite with over 2,900 resolved issues and more Node.js compatibility, but upgrading requires explicit opt-in due to breaking changes.
Engineers using Bun on Vercel Functions must explicitly set bunVersion to 1.4.x to upgrade, and should review breaking changes first. The Rust rewrite brings performance improvements and broader Node.js compatibility, but the opt-in requirement means existing deployments won't change automatically.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
Bun 1.4 is a rewrite from Zig to Rust, resolving over 2,900 issues and passing 1,500 additional Node.js compatibility tests.
To upgrade, set bunVersion to 1.4.x in vercel.json; it's an explicit opt-in due to breaking changes.
Bun 1.4 on Vercel Functions runs on Fluid compute with Active CPU pricing and supports WebSockets, Bun.serve(), and frameworks like Next.js, Elysia, and Hono.
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