2 Doomsday planes up right now. One of them is at 40,000 ft
https://global.adsbexchange.com/VirtualRadar/desktop.html
https://en.wikipedia.org/wiki/Doomsday_plane
Usually I see couple of kc-10a's but there are 9 at the moment. https://global.adsbexchange.com/VirtualRadar/desktop.html
KC-10 Extender: https://www.af.mil/About-Us/Fact-Sheets/Display/Article/104520/kc-10-extender/
9/54 are up.