> So in the end, it's really rare that any endpoints ever have "/v2" in the name.

This is an interesting empirical question - take the 100 most used HTTP APIs and see what they do for backward-incompatible changes and see what versions are available. Maybe an LLM could figure this out.

I've been just using the Dropbox API and it is, sure enough, on "v2". (although they save you a character in the URL by prefixing "/2/").

Interesting to see some of the choices in v1->v2,

https://www.dropbox.com/developers/reference/migration-guide

They use a spec language they developed called stone (https://github.com/dropbox/stone).