Migrating to Next.js 15: What Changed and How to Adapt

Next.js 15 introduced several breaking changes. Here is how to migrate your application without surprises.

Async Request APIs

The biggest change: cookies(), headers(), params, and searchParams are now asynchronous. Where you previously wrote const params = props.params, you now write const params = await props.params. This affects every dynamic page, layout, and route handler.

React 19 Compatibility

Next.js 15 ships with React 19 support. The new React compiler optimizes re-renders automatically. forwardRef is no longer needed — ref is a regular prop. useFormStatus and useActionState replace older form handling patterns.

Caching Changes

Fetch requests and GET route handlers are no longer cached by default. Previously, Next.js aggressively cached everything. Now you must opt into caching with force-cache or route segment config. This is a significant behavioral change that can affect performance if you relied on implicit caching.

Turbopack Stability

Turbopack is now the default development bundler. It is significantly faster than Webpack for large projects. If you have custom Webpack configurations, check Turbopack compatibility. You can opt out with --webpack if needed.

Migration Steps

Update package.json dependencies to Next.js 15 and React 19.

Run the codemod: npx @next/codemod@canary upgrade latest.

Fix remaining async API calls manually.

Review caching behavior and add explicit cache headers where needed.

Test thoroughly — focus on dynamic routes and data fetching.

Common Pitfalls

The codemod handles most changes but misses some edge cases in custom middleware and complex dynamic routes. Test your middleware, API routes, and any pages that use generateStaticParams carefully.