Dear @ajfinch - thanks for reaching out and apologies for the late response.
We are going to swap the major version number once RNTuple is production ready. That’s the technicality behind “ROOT 7”.
We are developing and releasing different parts at different pace, due to the need to focus our efforts. RDataFrame was one of the first elements to use the ROOT 7 style of interfaces; REve (2023), the web-based graphics system (2023), and RNtuple (2024) are on their way to production (respective release years). RHist development / a minimal viable product is planned for end of next year.
Does that help a bit? Is there something specific that you are after?
Cheers, Axel