Next.js 16 to 16.4: the upgrade notes we keep open

Next.js 16 shipped on 21 October 2025, and the team has released a minor roughly every two months since. 16.4 arrived on 6 October 2026. These are the changes we check on every client upgrade.

Turbopack is the default

Turbopack became stable and the default bundler for both next dev and next build. If a project depends on a custom webpack setup, you can still opt out with --webpack, but most of our builds simply got faster.

Cache Components and "use cache"

Caching is now explicit. With Cache Components switched on, everything is dynamic by default and you opt pages, components or functions into caching with the "use cache" directive. It completes the Partial Prerendering story: a static shell that loads instantly, with dynamic parts streamed in.

const nextConfig = {
  cacheComponents: true,
};
export default nextConfig;

revalidateTag() now takes a cache-life profile as a second argument, and two new Server Action helpers arrived: updateTag() for read-your-writes updates, and refresh() for uncached data.

'use server';
import { revalidateTag, updateTag } from 'next/cache';

revalidateTag('blog-posts', 'max');  // stale-while-revalidate
updateTag(`user-${id}`);         // user sees the change now

middleware.ts is now proxy.ts

The file that intercepts requests was renamed to make the network boundary clearer. Rename the file and the exported function; the logic stays the same. middleware.ts still works for Edge use cases but is deprecated.

export default function proxy(request: NextRequest) {
  return NextResponse.redirect(new URL('/home', request.url));
}

Breaking changes to plan for

• Node.js 20.9+ and TypeScript 5.1+ are required.
• params, searchParams, cookies() and headers() must be awaited.
• AMP and the next lint command were removed.
• next/image defaults changed, including a 4-hour minimum cache TTL.

16.1 to 16.4 in one minute

• 16.1 (Dec 2025): file-system caching for next dev went stable.
• 16.2 (Mar 2026): much faster dev startup, an AGENTS.md in new apps, and agent-friendly DevTools.
• 16.3 (Aug 2026): Instant Navigations, up to 90% less dev memory, first-party Skills, and docs available as Markdown.
• 16.4 (Oct 2026): lazy compilation, smaller bundles, React 19.3, and Cache Components on by default in create-next-app.

How we upgrade

# run the official codemod, then fix what it flags
npx @next/codemod@canary upgrade latest
npm run build

Then we test every route that reads cookies or params, check images, and only then flip on Cache Components route by route.