On Next.js 16 Turbopack is the default bundler for next dev and next build. Opt out with the --webpack flag.

Next.js 16 makes Turbopack the default bundler for both development and production builds with no configuration. You get faster Fast Refresh plus faster builds automatically. If you rely on a custom webpack setup you run next dev --webpack or next build --webpack. Turbopack dev had been stable and opt in before this release.