In true Valve fashion, Gaben & Co. have just launched the long-awaited Source 2 engine as part of the new Dota 2 Workshop Tools as ggmania reported today. Strangely Valve isn't confirming that this is actually Source 2 - but the Steam and Dota 2 communities are confident that this is it. You can also run an alpha version of Dota 2 in the new Source 2 engine, making it unofficially the first Source 2 game.

As ggmania reports:

Source 2 is mostly an optimization update. Those of us who've been using Hammer for a while will notice that the new Source 2 tool-set has (among other things) been massively optimized, especially in the way of file/folder directory set-up as well as the tools in general. It also takes advantage of DX 11, allowing for higher performance (and a better looking game in general). For those with 64 bit systems, it also really is useful due to the support of multi-core usage [finally!] (rendering times reduces, compile times reduced, etc.). It's essentially the same way Source is to Gldsrc (Half-Life 1 engine), except more subtle, since the graphical quality isn't changed as much.

So, where's Half-Life 3? We probably won't see a lot of fanfare or an "official" launch until there's a new triple-A game that uses the Source 2 engine and all of its glorious new features. This first official Source 2 game might well be Half-Life 3, though I wouldn't be surprised if it was TF3, L4D3, Portal 3, or some other game entirely.

Valve Source 2 has launched (apparently)