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Unreal Engine 4 (UE4) is Epic's next-generation technology, released in 2014. It provides a complete suite of game development tools made by game developers, for game developers. From 2D mobile games to console blockbusters, Unreal Engine 4 gives you everything you need to start, ship, grow and stand out from the crowd.
Unreal Engine 3 (UE3) was Epic's previous-generation technology that powered games on Xbox 360, PlayStation 3 and PC. This code has been proven in Gears of War 1,2,3 and Judgment and in Unreal Tournament 3 (formerly Unreal Tournament 2007). UE3 is no longer under active development.
Unreal Engine 2.5
Unreal Engine 2.5 (UE2.5) was the latest UE2 engine version for previous generation hardware. This code has been proven in Unreal Tournament 2004.
Unreal Engine 2 (UE2) was Epic's past-generation technology that supported DX8 and powered games on the following platforms: PC, Mac, Linux and the following consoles: Xbox, and PS2. This code has been proven in Unreal Tournament 2003, which was later transitioned to UE2.5. UE2 is no longer under active development.
Unreal Engine 2X
Unreal Engine 2X (UE2X) was a highly optimized version of Unreal Engine 2 only supported for Xbox, made for Unreal Championship 2. No further development continued for UE2X after UC2.