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Next.js 15.5: Node.js Middleware Is Stable, Turbopack Builds Are in Beta

webhani·

Next.js 15.5 shipped three changes that directly affect production codebases: Node.js middleware is now stable, Turbopack production builds are in beta, and TypeScript DX has meaningful improvements. Here's what each means in practice.

Node.js Middleware: What Actually Changed

Before 15.5, Next.js middleware ran exclusively on the Edge Runtime — fast and lightweight, but no access to Node.js APIs. fs, crypto, native modules, and many auth libraries were off-limits. If you needed those, you had to push logic into API routes and check results from middleware, which added latency and complexity.

With 15.5, middleware runs on the Node.js runtime by default. The full Node.js API surface is available.

// middleware.ts — full Node.js APIs now available
import { NextRequest, NextResponse } from 'next/server'
import { createHash } from 'crypto' // previously unavailable in middleware
 
export async function middleware(request: NextRequest) {
  const authHeader = request.headers.get('authorization')
 
  if (!authHeader?.startsWith('Bearer ')) {
    return NextResponse.json({ error: 'Missing token' }, { status: 401 })
  }
 
  const token = authHeader.slice(7)
 
  // crypto module works directly in middleware now
  const tokenHash = createHash('sha256').update(token).digest('hex')
  const isValid = await validateTokenHash(tokenHash)
 
  if (!isValid) {
    return NextResponse.redirect(new URL('/login', request.url))
  }
 
  return NextResponse.next()
}
 
export const config = {
  matcher: ['/api/:path*', '/dashboard/:path*']
}

The most impactful scenario is auth. JWT verification, session validation, and cryptographic checks that previously required a round-trip to an API route can now live in middleware where they belong.

Turbopack Production Builds

next build --turbopack is now available in beta. Vercel is already using it for vercel.com, v0.app, and nextjs.org.

# Enable Turbopack for production builds
next build --turbopack
// package.json
{
  "scripts": {
    "build": "next build --turbopack"
  }
}

Build speed improvements vary significantly by project size and configuration. Larger codebases with many modules benefit more. The Vercel team has reported meaningful reductions in preview deployment times.

Caveats: It's beta. Some webpack plugins and custom configurations may not be compatible. Before switching production builds, test in a CI environment with your full configuration. The --turbopack flag doesn't affect dev server behavior — that's already been Turbopack-powered since Next.js 15.0.

TypeScript DX Improvements

Typed Routes

Link href values are now validated at compile time. Navigating to a route that doesn't exist in your app is a type error.

// Compile error if /products/[id] doesn't exist as a route
<Link href="/products/123">View Product</Link>
 
// Typo — compile error
<Link href="/productz/123">Bad Link</Link>

Enable it in your config:

// next.config.ts
const nextConfig = {
  experimental: {
    typedRoutes: true // stable in 15.5
  }
}

Helper Types: PageProps, LayoutProps, RouteContext

// app/blog/[slug]/page.tsx
import type { PageProps } from 'next/types'
 
export default function BlogPost({ params, searchParams }: PageProps) {
  // params and searchParams are fully typed — no manual type annotation needed
  return <article>{params.slug}</article>
}
 
export async function generateMetadata({ params }: PageProps) {
  return {
    title: `Post: ${params.slug}`
  }
}

next typegen Command

Generate type artifacts without running a full build:

# Generates .next/types — much faster than a full build
npx next typegen

This is useful in CI to typecheck without the full build overhead.

Migration Considerations

If you have middleware that explicitly sets runtime = 'edge':

// Remove this to use Node.js runtime (default in 15.5)
export const runtime = 'edge'

For typed routes: enabling it on an existing codebase will surface every broken Link at once. Run npx next typegen first to see the scope, then fix iteratively rather than all at once.

Takeaway

Node.js middleware is the most practical change in 15.5 — it removes a whole class of workarounds. If your middleware currently delegates to an API route for auth logic, this is worth refactoring.

Turbopack production builds are worth testing in a staging environment now, with a clear plan to move to production once it exits beta.

Sources: Next.js Blog, InfoQ "Next.js 15.5 Ships", peerlist.io

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