The App Router is Now Default
Next.js 15 doubles down on the App Router paradigm. Server Components are first-class citizens, dramatically reducing client-side JavaScript and improving Time to First Byte.
Breaking Changes
params and searchParams are now Promises that must be awaited in Server Components. Cookie handling is now async. These changes improve security but require migration effort.
Turbopack Stable
The new Rust-based bundler is now stable for development builds, promising up to 10x faster HMR compared to webpack.