Not sure if these are a couple of TM employees but I read the following on Reddit:
"All 100% compatible T-Mobile compatible devices will be getting an OTA update between now and July, registering the devices on both networks, many of the newer devices are reporting it looks like T-MOBILE bands are the priority and they now fall back on the sprint network.
Which is ultimately the goal. Over half of sprints currently activated devices are 100% T-Mobile compatible. If they can get as many devices onto T-Mobile’s network now, it lessens the blow when they start network integration"
"The OTA will be for the SIM card and not the devices. What they will do is set the T-Mobile PLMN as the 2nd home network on the SIM cards and the devices will see the T-Mobile network as native."
From: https://www.reddit.com/r/Sprint/comments/g4aoxs/this_is_how_to_disable_sprint_bands_on_the_pixel/