This is all Epic has released so far via FAQ page:
"What are Unreal Engine 4’s system requirements?
You will need a powerful setup to get started developing with UE4 right now.
Here’s what we recommend:
Desktop PC or Mac
Windows 7 64-bit or Mac OS X 10.9.2 or later
Quad-core Intel or AMD processor, 2.5 GHz or faster
NVIDIA GeForce 470 GTX or AMD Radeon 6870 HD series card or higher
8 GB RAM"
It’s generally friendly to anything in the current gen of hardware i’m pretty sure, although i’m not sure about how it runs with windows 8. Keep in mind this is a newborn engine for us devs, we don’t have the wide amout of data to account for that yet.