pcworld[.]com/article/1477078/microsoft-will-stop-selling-windows-10-licenses-in-a-few-days.html
There are several articles today saying that Microsoft is going to stop selling Win10 in it's online store at the end of the month. The articles hint that the only remaining source for new licenses will be whatever 3rd party sellers have on hand, which might mean some closeout sales if you're after the retail version. Win7, 8, 10, & 11 keys however have all been *reported* to work interchangeably.