Well, historically, 4.0 was made to be roughly equivalent to 3.3 IIRC. 4.1 didn't add much and 4.2 started seeing changes going in the direction that was roughl

Well, historically, 4.0 was made to be roughly equivalent to 3.3 IIRC. 4.1 didn't add much and 4.2 started seeing changes going in the direction that was roughly complete by 4.5 I'd say. So each version bump in the 4.x range is just a history of getting a slightly cleaner API each version until you get to a version where you can personally say "I'm okay with this now" based on your preferences as a developer. For me personally that version is 4.3, it has the features where I think "this makes sense as an API" and things that came after that were just extra conveniences. But what are just conveniences for some developers are the basic core abstractions for other developers, and where you draw that line is up to you. In my personal opinion, 4.2 is like, halfway to 4.3 But sometimes it's more comfortable to go none of the way than half of the way, hence me targeting 4.0 in my most recent library.