The first version of next-sanity shipped with the picosanity client built-in. This caused some confusion for people who wants not only to pull data from their Sanity.io content lake, but also send patches and mutations via API routes. Since picosanity only supported fetching content, it had a smaller bundle size than the full SDK.
This version replaces picosanity with the full client. You can use Next.js' tree shaking to keep the client out of the app bundle or install picosanity if you still prefer to use that.