next breaking changes

• 15 \u2192 16api

  React Compiler stable (when enabled via experimental flag in 15, stable in 16).

  Migration

  Enable via `experimental.reactCompiler = true` in next.config.js. Reduces manual useMemo/useCallback.

• 15 \u2192 16build

  Turbopack is the default dev bundler. Webpack dev path still available via `--webpack`.

  Migration

  If you have custom webpack config for dev, either migrate to Turbopack rules or run `next dev --webpack`.

• 14 \u2192 15api

  params and searchParams in pages/layouts/route handlers are now Promises and must be awaited.

  Migration

  `export default async function Page({ params }) { const { id } = await params; }`. Use the `next-codemod` codemod `next-async-request-api`.

• 14 \u2192 15behavior

  fetch() is no longer cached by default in Route Handlers and Server Components. Opt-in via `cache: 'force-cache'` or `export const fetchCache = 'default-cache'`.

  Migration

  Audit fetches you relied on being cached. Explicit opt-in: `fetch(url, { cache: 'force-cache' })` or set `export const dynamic = 'force-static'`.

• 14 \u2192 15behavior

  GET Route Handlers are no longer cached by default. Client Router Cache no longer caches page components by default (staleTimes.dynamic defaults to 0).

  Migration

  To restore previous behavior set `experimental.staleTimes.dynamic = 30` in next.config.js or export `dynamic = 'force-static'` from route handlers.

• 14 \u2192 15removal

  @next/font package removed; use the built-in `next/font`.

  Migration

  `npm uninstall @next/font` and replace `from '@next/font/google'` with `from 'next/font/google'`.

• 14 \u2192 15runtime

  Minimum React version is 19 RC+ for App Router. Pages Router still supports React 18.

  Migration

  App Router: upgrade to React 19. Pages Router: stay on React 18 if needed, but new features target 19.

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