What I think they are referring to is the bundler is built with Go/Rust rather than JS (like Webpack). The difference in speed between Webpack and any bundler built in Rust/Go (SWC, Vite, Parcel, etc) is that the latter are like 10X faster, not "this is building faster" but "how the hell did it build this quick". That difference in speed is what I think of when they refer to "next generation".