Source 2

Source 2 is Valve's newest game engine. It improves on many things from Source. The first game to use Source 2 was Dota 2, which was ported in 2015 from Source. A port of Counter-Strike: Global Offensive has been announced, along with possible ports for every other Valve title.

Source 2 abandons much of the middleware that kept Source from being completely open to modding (in the form of exorbitant licensing fees). Valve's custom physics engine Rubikon replaces Havok.