Looks like CDMA Shutdown Day for Sprint is 1/1/22 or thereabouts, per this letter I got from T-Mobile.

I'm curious how much of Sprint's LTE network will be online at that point. Betting that on 1/1/22 it'll be down to the PCS G block plus B26. pic.twitter.com/dMan26HLox

— Ian Littman (@iansltx) December 27, 2020