A Microsoft spokesman confirmed the two-to-four-year stretch, saying in an email exchange last week that, "The upgrades will be for [the] life of device, which we estimate to be 2 to 4 years." But the company has not detailed exactly who gets just two years of updates and upgrades, who gets four, and who gets something in-between.
Microsoft has also not yet refreshed its Windows lifecycle support page to include Windows 10.
Other sections of the Windows 10 EULA lay out transfer rights -- whether the OS can be moved to another device -- and "downgrades," the right to install an older edition of Windows on a new device that came with Windows 10. Both of those sections are identical to prior editions' licenses: Users can downgrade from Windows 10 Pro only, for example, and then only to Windows 7 Professional or Windows 8.1 Pro.
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