But `use` is still just in the RFC phase, right? How can Next.js already be (committing to) using it?

They’re essentially both in beta, but for something like this, React needs a proving ground - hence it’s being used in Next’s beta functionality

Oh! I'd mis-parsed the heading sizes, didn't realise the "data fetching" heading was underneath the "app/ directory (beta)" heading, and thus that they were both in beta. Thanks!