params Is a Promise Now

Dynamic APIs in the App Router are async. params, searchParams, cookies(), and headers() all return promises, and reading them synchronously is a type error before it is a runtime one.

The shape every dynamic route now takes:

export default async function Page({
  params,
}: {
  params: Promise<{ slug: string }>
}) {
  const { slug } = await params
  return <Article slug={slug} />
}

generateMetadata takes the same treatment, and so does searchParams:

export default async function Page({
  searchParams,
}: {
  searchParams: Promise<{ q?: string }>
}) {
  const { q } = await searchParams
}

Two things worth knowing:

• The page function has to be async to await them. Static pages that never touched async are the ones this catches.
• Awaiting searchParams opts the route into dynamic rendering. If a param is only used for a redirect, that cost is real — check whether it belongs in the route segment instead.

The mechanical fix is a Promise<> wrapper and an await. The thing actually worth reading is the upgrade guide, because this rarely arrives alone.