Word is going around that the anticipated Windows 10 Fall Update will be released in November. Codenamed "Threshold 2", this will be the first major update to Windows 10 and it's believed to carry version number 1511.
Windows 10 Fall Update will not require any other updates to be installed first, you can upgrade straight to Windows 10 Fall Update from the RTM (release-to-manufacturing) version of Windows 10, and if you're still using Windows 7/8.1 you'll be able to upgrade straight to Windows 10 Fall Update without having to install Windows 10 first.
SuperSite for Windows reports the update will be distributed via Windows Update, and notes that on new installs, Windows 10 Fall Update will support activating your PC using Windows 7, 8 or 8.1 product keys.
Windows Update distribution. You will get the Windows 10 Fall Update the same way you get any other Windows 10 update: Through Windows Update. It will have the same distribution as a security update, meaning that you will get it immediately. Ideally, you will just wake up the PC one day, sign-in, and already be on the new version. The update will be named “Windows 10 November 2015” in Windows Update.
Activation changes. As previously reported, Windows 10 Fall Update will support activating with your PC’s Windows 7, 8, or 8.1 product key. For this to work, the key must match the edition of Windows 10 using the same upgrade matrix.
Other than that, Windows 10 Fall Update will include updates for Cortana, an improved Media Creation Tool, Edge browser enhancements, and a couple of new features like texting from the desktop. The update will also update the recovery tools so Windows 10's push-button reset recovery feature resets your PC to Windows 10 Fall Update instead of July's RTM release.