How can we solve type inference errors in Next.js 16 TypeScript configs for API routes?

Type inference errors in Next.js 16 TypeScript API routes usually happen because dynamic params now return Promises, causing mismatches in route handlers like GET/POST. Fixing this involves proper Promise typing and awaiting params.​

The main issue stems from Next.js 15+ changes where dynamic route params in API routes (app/api/[id]/route.ts) are async Promises, not plain objects—TypeScript flags this during build/deploy but not always in dev. Solve it by typing the context as { params: Promise<{ id: string }> } and awaiting the params inside your handler. Enable typedRoutes: true in next.config.ts for better route-aware type helpers that auto-generate accurate types during next dev or next build. This ensures full end-to-end type safety without hacks like any or ESLint disables.

Code

// next.config.ts
const nextConfig = {
  typescript: {
	typedRoutes: true,
  },
};

export default nextConfig;


// app/api/users/[id]/route.ts
import { NextRequest, NextResponse } from 'next/server';

export async function GET(
  request: NextRequest,
  { params }: { params: Promise<{ id: string }> }
) {
  const { id } = await params;

  const user = await getUser(id);

  return NextResponse.json(user);
}