The Insider Preview releases of Windows 10 didn't include any way to prevent Windows Update from downloading and installing updates, but it wasn't clear if this was just some quirk of the previews or the long-term plan; Microsoft's previews often have special rules for things like providing automated feedback and hooking up online services, and so this could have been part of that.
Build 10240, released to insiders on Wednesday, changes that. This build is believed to be the release-to-manufacturing build that OEMs will preinstall on hardware, and as such, it contains the finalized settings, license text, and so on.
Windows Update in Windows 8.1 has four options for Windows Update's behavior: download and install updates automatically; download updates automatically but choose when to install them; check for updates but choose when to download and install them; and never check for, download, or install updates. This last option is, obviously, not recommended, but it's there if you really need it.
In Windows 10, the options are cut to two: check, download, install, and reboot automatically; and check, download, install automatically and then choose to reboot. And as Tim Anderson at The Register spotted, the EULA that comes with the operating system (and which again wasn't available during the preview program, as that used a different, preview-specific text) has language that supports this:
Updates. The software periodically checks for system and app updates, and downloads and installs them for you. You may obtain updates only from Microsoft or authorized sources, and Microsoft may need to update your system to provide you with those updates. By accepting this agreement, you agree to receive these types of automatic updates without any additional notice.
Source: http://arstechnica.com/information-tech ... ome-users/