nextjs-16-noteslisted

# Next.js 16 — current stable major Current stable major of Next.js, now at 16.2.x. > Version floors: **Node.js 20.9.0+** (Node 18 dropped), **TypeScript > 5.1.0+**, **React 18.2.0+ or 19**. React 19 is recommended and is > the default for new apps, but it is NOT required — a React 18.3.1 > app adopts Next.js 16 without a React major upgrade. For > React-language guidance, pair this cross-stack with the `react-18` > or `react-19` module. --- ## Signature features ### Turbopack by default Turbopack is the default bundler for both `next dev` and `next build` in 16 — no `--turbopack` flag needed anymore, and its absence no longer means webpack. Opt out with `--webpack`: ```json { "scripts": { "dev": "next dev", "build": "next build" } } ``` ```bash next build --webpack # opt out of Turbopack ``` ### `next upgrade` CLI Added in 16.1.0 — an automated upgrade helper: ```bash next upgrade ``` The general codemod runner still applies for broader migrations: ```bash npx @next/codemod@canary upgrade latest ``` --- ## Migration traps Ordered by blocker severity, most severe first. ### 1. Async-only Request APIs (the biggest code-level break) `params`, `searchParams`, `cookies`, `headers`, and `draftMode` are now **async-only** (Promises). The temporary synchronous compatibility shim from v15 is fully removed in 16. Code written against 14-era synchronous props hits this first: ```tsx // 14-era — no longer works export default function Page({ params }: {