Epic released this last week :
"Today, Epic has opened up Unreal Engine 4 to the world! UE4 is now available for download in its entirety, including the full features, tools and the entire C++ source code for PC, Mac, iOS, and Android through a subscription plan. You can subscribe to UE4 for $19 per month, and ship games with UE4 commercially by paying 5% of gross revenue from product sales to users.
The engine includes lots of free content, including template games, sample games, content examples and more from the built-in Marketplace.
To get started, visit https://www.unrealengine.com."