Next.js 14 -> 15 Migration Instructions for LLM

Migrate the Nx workspace's Next.js projects from 14 to 15. Run the codemod first, fix the rest by hand, build after each project.

Step 1: Codemod

bash

npx @next/codemod@canary upgrade 15

Pin to 15 (not latest - that now resolves to 16). The @canary tag is what Next ships the upgrade codemod on. Handles most async-API rewrites. Review the diff.

Step 2: React 19 (App Router only)

Next 15 App Router requires React 19. Page Router can stay on React 18. For App Router projects, also run the React 18 -> 19 migration.

Step 3: Async request APIs (main breaking change)

cookies, headers, draftMode, params, searchParams are now async. Codemod covers most; fix leftovers.

tsx

// before
const { slug } = params;
// after
const { slug } = await props.params;

Make the component / handler async and await the value.

App Router only - Pages Router getServerSideProps / getStaticProps / getStaticPaths context.params is NOT async; leave it unchanged.

Step 4: Caching defaults changed

No longer cached by default: fetch, GET route handlers, client navigations. Re-add caching where you relied on it.

fetch(url, { cache: 'force-cache' })
Route handler: export const dynamic = 'force-static'

Step 5: Misc

@next/font removed -> import from next/font.
Route runtime: 'experimental-edge' -> runtime: 'edge'.
next.config renames: experimental.bundlePagesExternals -> top-level bundlePagesRouterDependencies; experimental.serverComponentsExternalPackages -> top-level serverExternalPackages.
NextRequest.geo / request.ip removed (e.g. in middleware) -> read from headers (x-forwarded-for, platform geo headers).

Validate

bash

nx run PROJECT:build
nx affected -t build,lint,test

Notes for LLM

Codemod first, then manual.
One project at a time, build after each.
Skip Step 2 for Page Router projects.