Bun vs Node.js for Next.js: Real Benchmark Results

Bun vs Node.js for Next.js: What the Numbers Actually Say

Honestly, Bun gets overhyped. Every six months there's a new blog post claiming it'll replace Node.js entirely, with benchmarks that conveniently test synthetic HTTP servers rather than real applications. So I ran my own tests on a Next.js 15.1.0 app using both Node.js 22.4.0 and Bun 1.1.38 — same codebase, same machine, same environment.

The short version: Bun is genuinely faster at some things, slower at others, and has real compatibility gaps you'll hit in production. If you're making a runtime decision for a serious Next.js project, you need the full picture, not a cherry-picked npm install timing.

My test app was a mid-sized Next.js project: 47 routes, App Router, Prisma with a PostgreSQL backend, three API routes using server actions, and about 120 npm packages. Nothing exotic. The kind of project you'd actually ship.

Install Speed: Where Bun Genuinely Wins

Cold install on a clean node_modules — no cache, no lockfile tricks. Node.js + npm 10.8.2 took 34.2 seconds. pnpm 9.1.0 dropped that to 18.7 seconds. Bun 1.1.38 finished in 4.1 seconds. That's not a typo.

Warm installs (cache present, lockfile intact) are even more dramatic. Bun averages around 400ms to verify and relink 120 packages. npm takes about 8 seconds for the same operation. If you're running installs in CI on every PR, that gap compounds fast. If you're working on a project where comparing package managers is already on your radar, Bun's install speed alone might justify switching.

That said, lockfile compatibility is still a real concern. bun.lockb is binary and not human-readable. If your team mixes runtimes or you're integrating with tools that parse lockfiles, you'll need --save-text-lockfile to keep a bun.lock file alongside it. Minor friction, but friction.

Dev Server Cold Start: Next.js 15 with Both Runtimes

This is the one developers care about most day-to-day. Time from next dev to first page served. On Node.js 22.4.0, my test app cold-started in 3.8 seconds. On Bun 1.1.38, it came in at 3.1 seconds. Roughly 18% faster. Noticeable, but not the 3x improvement you'll see claimed elsewhere.

Hot reload after a component change was where I expected Bun to shine, given its native transpiler. In practice, both runtimes averaged 280–320ms for a server component change and 90–140ms for a client component. The difference was inside margin of error on repeat runs. Next.js's own Turbopack compiler is the bottleneck here, not the JavaScript runtime underneath.

Worth noting: next dev --turbo (Turbopack) behaved identically between runtimes for hot reload. Turbopack offloads transpilation to Rust regardless of whether Node.js or Bun is running the process. So if you're already on Turbopack, the dev server argument for Bun weakens considerably.

Production Build Times and Bundle Output

Running next build on Node.js 22.4.0 took 41.3 seconds. On Bun 1.1.38, it took 38.9 seconds. About 6% faster. Honestly, not worth migrating a project for. The build is dominated by Next.js's own compilation pipeline, not runtime I/O.

Bundle sizes were identical — same webpack output, same chunk sizes. Bun doesn't replace Next.js's bundler, it just runs the Node.js-compatible scripts around it. If you're looking for bundle optimization wins, comparing Vite against Next.js is a more relevant conversation than swapping runtimes.

Memory usage during build was slightly lower with Bun — peaked at 1.2GB vs 1.4GB on Node.js for this project. If you're running builds on memory-constrained CI runners (say, 2GB limit), that margin could matter.

API Route Performance: The Benchmark That Actually Matters

This is where things get interesting. I benchmarked a simple API route that reads from PostgreSQL via Prisma, formats a response, and returns JSON. Under load with autocannon -c 50 -d 10 (50 concurrent connections, 10 seconds):

// app/api/users/route.ts — tested under both runtimes
import { db } from '@/lib/db'
import { NextResponse } from 'next/server'

export async function GET() {
  const users = await db.user.findMany({
    select: { id: true, name: true, createdAt: true },
    take: 20,
  })
  return NextResponse.json(users)
}

// Results (autocannon -c 50 -d 10s):
// Node.js 22.4.0: 1,847 req/s  — avg latency 26.8ms
// Bun 1.1.38:     1,912 req/s  — avg latency 25.9ms

About 3.5% faster on Bun for a real database-backed route. Meaningful? Marginally. The Prisma client, PostgreSQL round-trips, and Next.js middleware are the bottlenecks — not V8 vs JavaScriptCore. For I/O-bound workloads, which is most Next.js API work, both runtimes are essentially equivalent.

Compatibility Issues You'll Actually Hit

Here's the honest part of the article. Bun 1.1.38 still has gaps. sharp for image processing needs explicit install flags and sometimes a native rebuild. better-sqlite3 works fine. Some Jest configurations need migration to Bun's built-in test runner. And crypto.randomUUID() behavior has edge cases that bit me in middleware.

Prisma works, but you need bun add prisma@latest and to confirm your schema.prisma generator target is node not bun for the client — otherwise you get subtle type generation issues. Docker images also need attention: official Bun images are oven/bun:1.1.38-alpine and they're well-maintained, but your multi-stage Dockerfiles will need updating.

Is it worth the migration friction for an existing app? Probably not unless install speed or a specific performance bottleneck is actually hurting you. For a greenfield project? Bun is stable enough to start with in 2026. Just read the compatibility table before you assume all your native addons will work. And if you're also evaluating your overall tech stack, articles like Next.js vs Astro for 2026 cover the bigger runtime-adjacent decisions.

Setting Up Next.js with Bun: The Actual Commands

If you want to try it, here's the setup that actually works as of Bun 1.1.38 and Next.js 15.1.0. Don't trust tutorials from early 2024 — several flags and config options have changed.

# Create new Next.js project with Bun
bun create next-app@latest my-app --typescript --tailwind --app --src-dir
cd my-app

# Install with Bun (creates bun.lockb)
bun install

# Dev server — works identically to npm run dev
bun dev

# Build
bun run build

# If you need human-readable lockfile for CI tooling
bun install --save-text-lockfile

# package.json scripts work as-is, no changes needed
# Bun reads them the same way Node does

One gotcha: bun dev uses Bun's own script runner, which is faster than npm run dev but skips some npm lifecycle hooks. If your project relies on predev scripts, verify they fire correctly. For most projects they do, but it's worth a quick check.

Should You Switch Your Next.js Project to Bun?

New project starting today? Use Bun. The install speed alone makes it worth it in CI, and compatibility in late 2026 is solid enough for standard Next.js stacks. You'll save 20–30 seconds per CI run. Over a year that adds up.

Existing production app? Be more careful. Audit your native dependencies first — run bun pm ls | grep native and check each one against Bun's compatibility list. If you're using anything with complex native bindings (canvas, some ML packages, certain database drivers), plan for a week of testing, not an afternoon.

What about the performance case? For most Next.js apps, the runtime isn't your bottleneck. Your database queries are. Your third-party API calls are. Switching from Node.js to Bun won't make a slow Prisma query fast. It also won't break a fast one. If you're building something performance-sensitive and want a broader comparison, checking how Empire UI components benchmark across frameworks gives useful context for where rendering costs actually land. The runtime choice matters less than you think once your app is doing real work.

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