HOW TO:
To launch dota 2, which works under Source 2 engine first you have to download DOTA 2 Workshop Tools from steam platform. Than launch newest file DOTA2.EXE localized in Steam\steamapps\common\dota 2 beta\dota_ugc\game\bin\win64
Newest engine is compatible with older brother SOURCE 1. In Dota 2 you can notice only very minor cosmetic graphic changes. On top of that, dota launches in newest 64bit version. It is faster and probably more stable itteration.
Keep in mind it is in alpha version.