What to Know Before Migrating to Next.js 16 Beta

What's New in Next.js 15.5 and the 16 Beta

Next.js 15.5 shipped Turbopack builds in beta, stable Node.js middleware support, TypeScript config improvements, and deprecation warnings for next lint. Next.js 16 beta is now available, previewing larger changes to routing and the developer experience.

The most meaningful shift for most teams is Turbopack reaching production build support.

Turbopack Production Builds

Turbopack has been the default dev server bundler since Next.js 15. The addition of production build support in 15.5 (beta) closes the last significant gap between Turbopack and Webpack.

Performance numbers on large codebases are substantial:

The dev server improvements have been available since Next.js 15. The production build improvement is the new piece — and it matters most for CI/CD pipeline duration.

Stable Node.js Middleware

The edge runtime constraint on middleware has been a long-standing frustration. As of Next.js 15.5, middleware runs stably on the Node.js runtime, which means full access to Node.js APIs — including crypto, streams, and third-party packages with native dependencies.

// middleware.ts — Node.js runtime (Next.js 15.5+)
import { NextRequest, NextResponse } from 'next/server';
import { verifyJwt } from './lib/auth'; // Node.js crypto dependency — works now
 
export async function middleware(req: NextRequest) {
  const token = req.cookies.get('session')?.value;
 
  if (!token) {
    return NextResponse.redirect(new URL('/login', req.url));
  }
 
  const payload = await verifyJwt(token);
  if (!payload) {
    return NextResponse.redirect(new URL('/login', req.url));
  }
 
  return NextResponse.next();
}
 
export const config = {
  matcher: ['/dashboard/:path*', '/api/:path*'],
};

This removes the workarounds many teams had in place — route handlers or custom servers just to run Node.js crypto in auth middleware.

The next lint Deprecation

next lint is being deprecated in favor of managing ESLint directly. The migration is straightforward but requires updating your project's lint setup before you upgrade.

// eslint.config.js (flat config format)
import { FlatCompat } from '@eslint/eslintrc';
 
const compat = new FlatCompat();
 
export default [
  ...compat.extends('next/core-web-vitals'),
  {
    rules: {
      // your custom rules
    },
  },
];

Check your package.json scripts and CI configs — anything calling next lint directly will need updating.

Migration Considerations

Turbopack production builds are still beta. Before switching from Webpack to Turbopack for production:

• Test builds locally with next build --turbopack
• Watch for issues with custom Webpack loaders or plugins
• Measure actual build times in CI, not just locally

React 19 Server/Client component boundaries become more important. Next.js 16 assumes React 19. If you haven't been deliberate about 'use client' boundaries, now is the time:

// Default: Server Component
// runs on the server, can be async, access databases directly
async function ProductPage({ id }: { id: string }) {
  const product = await db.products.findById(id);
  return <ProductView product={product} />;
}
 
// Explicit: Client Component
'use client';
import { useState } from 'react';
 
function ProductView({ product }: { product: Product }) {
  const [quantity, setQuantity] = useState(1);
  // browser state and events are fine here
}

Takeaway

Next.js 16 is a meaningful update, but the path to adoption should be incremental:

1. Migrate next lint to direct ESLint config now
2. Confirm your middleware works on Node.js runtime
3. Test Turbopack production builds in a staging environment
4. Hold off on Next.js 16 beta for production until stable release

The dev server already benefits from Turbopack in Next.js 15 — so the main gain waiting in 16 for most teams is production build speed.