Next.js 15 vs 14: Every Breaking Change and How to Upgrade

Update (June 2026): Next.js 16 is now the current stable release — 16.2.7 on npm as of June 10. This guide covers the 14 to 15 migration, which is still the required first step if you are on 14 or older. For the current version and the 15 to 16 path, see Next.js Latest Version June 2026.

Next.js 15 builds on the App Router and React 19 support introduced in earlier versions. If you are on Next.js 14 and wondering whether to upgrade, here is what changed and how to decide.

What Changed in Next.js 15

React 19 and React Compiler. Next.js 15 targets React 19 and supports the React Compiler (optional) for automatic memoization. If you are still on React 18, you will need to upgrade React first.

Caching behaviour. fetch() is no longer cached by default. This is a breaking change for code that relied on default caching. You can opt in with the cache option. Same for Route Handlers and Client Router Cache: review the docs for the new defaults.

Async Request APIs. request.cookies and request.headers can be async in certain contexts. If you use them, you may need to await them. The upgrade guide lists the exact APIs.

Turbopack. Turbopack is stable for development. You can run next dev --turbopack for faster local iteration. Production builds still use Webpack by default unless you opt into Turbopack for production when available.

Other improvements. Better error messages, partial prerendering (experimental), and continued improvements to the App Router and Server Components. Check the official release notes for the full list.

Breaking Changes to Watch

• Caching: If your app relied on default fetch caching, add explicit cache or revalidate options.
• React version: Ensure compatibility with React 19 (or the minimum version required by Next.js 15).
• Async APIs: Await request.cookies/headers where required.
• Deprecations: Run the upgrade and fix any deprecation warnings; some APIs may be removed in a future major.

Should You Upgrade?

New projects: Start with Next.js 15 (and React 19 if you want the latest). You get the new defaults and features from day one.

Existing Next.js 14 apps: Upgrade when you have time to test and fix caching and async API usage. The migration is usually manageable if you follow the upgrade guide and run tests. If you are in a freeze period, staying on 14 is fine until you are ready.

Stability-first teams: Wait for the first minor (e.g. 15.1) if you prefer to let early adopters find the rough edges. Next.js 14 remains supported.

In short: Next.js 15 is the right choice for new apps and for teams ready to adopt new caching and React 19. For existing apps, plan an upgrade when you can test thoroughly and handle the breaking changes.