Microsoft link here
Today, we are thrilled to announce Windows 11 will start to become available on October 5, 2021. On this day, the free upgrade to Windows 11 will begin rolling out to eligible Windows 10 PCs and PCs that come pre-loaded with Windows 11 will start to become available for purchase. A new Windows experience, Windows 11 is designed to bring you closer to what you love.
As the PC continues to play a more central role in our lives than ever before — Windows 11 is ready to empower your productivity and inspire your creativity.
Found this at OzBargain
From what I can recall when we went from Win7 to Win10, we upgraded many client PCs, then wiped them, and put Win7 back on. This meant that the digital license for Win10 was validated and would work down the track once the client was ready to move on, even if they didn't want to change over at that point (they were probably on WinServer 2008R2 and would have waited until going to WinServer 2016).
I wouldn't necessarily do that on a machine that was already in use and running fine, but if you regularly wipe machines anyway and re-install, might be worth doing it next time, and you could do it on any 'hot spares' that you have lying around ready to go 'in case'.
I haven't looked, but I am guessing there is no specific end date by when the Win10 to Win11 upgrade rights need to be exercised or lost. Last time I tried upgrading a Win7 to Win10, which was probably well over a year ago, maybe much more, it could still be done, which might have been five years from it first being made available, so this one might last for a long time too, but no guarantees.
Alan.