I have only twice seen a service ever make a /v2.

It's typically to declare bankruptcy on the entirety of /v1 and force eventual migration of everyone onto /v2 (if that's even possible).

A lot of the Unix/Linux Syscall api has a version 2+

For example dup(), dup2(), dup3() and pipe(), pipe2() etc

LWN has an article: https://lwn.net/Articles/585415/

It talks about avoiding this by designing future APIs using a flags bitmask to allow API to be extended in future.

I work for a company that has an older api so it's defined in the header, but we're up to v6 at this point. Very useful for changes that have happened over the years.

Isn’t having the name (e.g. Over2gb) easier to understand than just saying v2? This is in the situation where there is breaking changes forced upon v1/downloadFile.