[Kolossus]

I've seen on the Unreal site that the UDK (aka Unreal Engine 3) is free, while the UE4 is subscription based. Would that be ok as well to map for UrT HD?

Are the differences between the two kits that huge to avoid the use of the previous kit? Based on my experience (Blender, etc) a newer version doesn't necessarily mean drastic changes so I was wondering if someone could enlighten me on this.

[rayne2]

You can practice in UE3 but can't use it to build maps for UrT HD.

UE4 isn't just a newer version, it's a completely new thing. So they're not compatible.

[FS HappyDay]

It's not simply a new version of the same tool, it's a new tool for a new engine. UDK is the level editor for unreal engine 3 games, whereas the current unreal engine 4 editor is referred to as UE4. In principle they work pretty much the same way. However, content is not easily transferred from udk to ue4. You have to redo everything in ue4. You could use the free udk to check out some stuff that wasn't possible with radiant/id tech 3 engine but you might as well pay 19 $/€ and get started with the real deal.