Next.js 15.5: Turbopack Builds Beta and Node.js Middleware Stable

What Changed in Next.js 15.5

Two changes stand out in Next.js 15.5:

Turbopack builds hit beta — next build --turbopack is now a supported option for production builds
Node.js Middleware is stable — Middleware no longer runs on the Edge Runtime, so you get full Node.js API access

There are also TypeScript improvements — typed routes and route export validation — plus early deprecation warnings targeting Next.js 16.

Turbopack Builds: From Dev to Production

Until 15.5, Turbopack was limited to the development server (next dev --turbopack). Now it extends to production builds:

# Run a Turbopack build
next build --turbopack
 
# Or add it to package.json
# {
#   "scripts": {
#     "build": "next build --turbopack"
#   }
# }

For large projects, Turbopack can reduce build times significantly compared to Webpack. The beta label means it's ready for testing and CI profiling, but production adoption should wait until you've validated compatibility with your plugin stack.

What to check before switching

Webpack plugins with no Turbopack equivalent will fail or be silently skipped
Custom loaders may behave differently — test your entire bundle output, not just a smoke test
next lint is deprecated in 15.5 — move to direct ESLint configuration if you haven't already

Node.js Middleware is Now Stable

The old Edge Runtime constraint in Next.js Middleware was a persistent friction point. If you needed crypto, bcrypt, or any module that touches the file system, you had to push the logic out to an API route. That changes in 15.5:

// middleware.ts — full Node.js access in 15.5
import { NextRequest, NextResponse } from "next/server";
import { createHash } from "crypto"; // Previously unavailable in Edge Runtime
 
export function middleware(request: NextRequest) {
  const token = request.cookies.get("session")?.value ?? "";
  const hash = createHash("sha256").update(token).digest("hex");
 
  const response = NextResponse.next();
  response.headers.set("x-session-hash", hash);
  return response;
}
 
export const config = {
  matcher: ["/api/:path*", "/dashboard/:path*"],
};

This unlocks cleaner auth middleware patterns, session validation, and request transformation logic that previously required an extra API hop.

TypeScript Improvements

Typed Routes Enable experimental.typedRoutes in next.config.mjs and <Link href> / router.push() will accept only valid routes as defined by your file-based routing.

// next.config.mjs
const nextConfig = {
  experimental: {
    typedRoutes: true,
  },
};

// ✅ Valid — /dashboard exists in your file structure
<Link href="/dashboard">Dashboard</Link>
 
// ❌ TypeScript error — /dashbord does not exist
<Link href="/dashbord">Dashboard</Link>

Route Export Validation Invalid exports from page components or route handlers now produce build-time errors rather than silent failures. This catches issues like exporting unexpected named functions from a page file.

Next.js 16 Deprecation Warnings

15.5 adds warnings for patterns that will break in Next.js 16. Run a build and pipe it through grep to see what needs attention:

next build 2>&1 | grep -i "warn\|deprecated"

Addressing these now avoids a time-pressured upgrade later.

Our Take

Node.js Middleware going stable is the most immediately useful change in this release. The Edge Runtime limitation was a real constraint in production auth setups, and removing it simplifies middleware architecture considerably.

Turbopack builds are worth profiling in CI now — build time data collected during the beta phase will inform a smoother migration when it reaches stable.

Takeaways

next build --turbopack is beta — test before adopting in production
Node.js Middleware is stable — crypto, full Node.js APIs are now available
Typed routes add compile-time safety to navigation
Route export validation catches more bugs at build time
next lint is deprecated — migrate to direct ESLint config
Review deprecation warnings for the upcoming Next.js 16 upgrade