Come up with a decent API design from the beginning; commit to backwards compatibility, non-breaking changes, thorough testing and fast fixes; and stick with it for a decade or so.
No function should be promoted to the core API without serious consideration. Instead use something like /alpha/function-v2.2/ for testing functions that may disappear or be updated, making it easy for clients to write workarounds for these non permanent functions.
Yes, you can try and put it off for as long as possible, only making backwards compatible changes. But it's likely at some point you'll need to change something in your API, that simply won't work with existing clients.