Can someone remind me again what kind of fare I need to look for if I'm looking for upgrades with miles on an international itinerary. Is it Y M B?

It's been quite a while since I attempted something like this, but I remember I call in to see if upgrades are available and then I buy the fare (in those days M fare). I thought I read somewhere that other fares are now also eligible for upgrade with miles, like T fare. Is this true or is it only for elites? (No status anymore.)

ETA and please point me to the correct page on this site, or the Delta site, if that is available. Thank you.