8.1

[phrankco]

Install Windows 8.1 Update to continue receiving patches after April 8, 2014
Buy Windows 8.1 - Microsoft Store
Already running Windows 8? No need to buy Windows 8.1—you can update to Windows 8.1 for free through the Windows Store.
Buy Windows - Microsoft Windows

 

[BK_123]

I am pretty sure that everyone would've known about this..

 

[strollin]

No, not everyone would've known this, especially since this is misleading and inaccurate. It isn't Win 8.1 that is required but the Win 8.1 update 1 that will be required in order to receive future updates. That means someone running Win 8 needs to first upgrade to Win 8.1 as the OP stated but then also needs to ensure that the Win 8.1 update 1 gets installed as well.

Many people are confusing the two but they are distinct updates.