params.id is undefined after upgrading to Next.js 16 because params and searchParams are Promises

Symptom

params.slug is undefined in a page that worked on Next.js 14Route "/blog/[slug]" used `params.slug`. `params` is a Promise and must be unwrapped with `await` or `React.use()` before accessing its propertiesProperty 'slug' does not exist on type 'Promise

Cause

Next.js 15 turned params, searchParams, cookies(), headers() and draftMode() into Promises but kept a synchronous fallback with a warning. Next.js 16 removed that fallback, so property reads on the raw prop return undefined.

Fix

Await the prop in Server Components and unwrap it with React.use() in Client Components. Run the async request API codemod, since the general upgrade codemod skips it.

ApplyCopy

npx @next/codemod@canary next-async-request-api . export default async function Page(props: PageProps<'/blog/[slug]'>) { const { slug } = await props.params }

Affected

Next.js 15 (warning) and 16 (sync access removed); also opengraph-image, icon and sitemap id params in 16

Sources

• https://nextjs.org/docs/app/guides/upgrading/version-16
• https://nextjs.org/docs/messages/sync-dynamic-apis
• https://github.com/vercel/next.js/issues/74406

Last verified 2026-10-15 · Confirmed by 0 builders