The new Next.js client is built using the SWR (Server-Side Rendering) library, which provides a more efficient and optimized data fetching experience. The client supports queries, subscriptions, and mutations, with features such as optimistic updates, invalidation of queries after mutations, and support for Server-Side Rendering (SSR). The API is fully typed and uses middleware to add functionality to individual hooks or globally using `SWRConfig`. The new client also works seamlessly with live queries and subscriptions, making it an excellent choice for building high-performance APIs. With the release of SWR 2.0RC, the Next.js client has been rewritten to use SWR, providing a more streamlined experience for developers.