In a alpha update to Dota 2's workshop tools it appears as if valve has updated the now ten year old source engine.
"Everything that would share a name with Source is named '...2'. That's 'engine2.dll', 'vconsole2.exe', 'vphysics2.dll'."
This update includes an updated version of hammer editor, a new way of handling DLLs, and a hole lot of 2s.
http://goo.gl/4WzICB
Source: http://goo.gl/4WzICB