Next.js 16 Async params/cookies/headers; opt-in caching via "use cache"; Turbopack default.
Anti-patterns:
❌ Sync request APIs; ✅ await params, cookies(), and headers(). ❌ Keep middleware.ts; ✅ use proxy.ts and export function proxy. ❌ revalidateTag("posts"); ✅ revalidateTag("posts", "max") or { expire: ... }.
References: references/migration-checklist.md, references/cache-components.md, references/turbopack.md