Microsoft provides the Windows 8.1 SDK primarily through its official archive and legacy portals:
When you download the Windows 8.1 SDK, you gain access to several critical components: windows 8.1 sdk download
The safest place to download the standalone installer is the Windows SDK Downloads Archive . Microsoft provides the Windows 8
Here’s a good feature breakdown for the download, focusing on what makes it useful even today for specific development scenarios. windows 8.1 sdk download