http://i.imgur.com/IwAmjjp.jpg

I shall say no more but I think these reddit users broke the NDA they signed

So the Steamworks SDK was open to the public this week which led to some new information regarding source2 to emerge.
First bit of information was relating to “Left 4 Dead 3” found by DevinWatson as he posted this picture on facepunch
http://abload.de/img/362bcwoe8w.jpg
DevinWatson said “I brute forced it in a way, there were lots of interesting things I found. L4D3 was the most interesting although it hasn't been updated in months so it may be dead. Fun fact TurboTax is coming to Steam”
There have been other information regarding source2 as some former Valve developers have added “Source2” to their LinkedIn profiles.

Readmore
http://www.neogaf.com/forum/showthread.php?t=573769

Tom Leonard, former Valve employee, may have let slip the existence of the much rumoured 'Source 2' Engine, via an entry on his LinkedIn profile.
http://www.linkedin.com/pub/tom-leonard/0/86b/493?trk=pub-pbmap

Leonard was fired, or 'released' as Valve would prefer to say, last month.

Leonard's work at Valve includes Left 4 Dead 2 and Portal 2 and, going back further, Half Life 2 and the subsequent Orange Box. He was employed there a long time it seems and his LinkedIn profile lists his role as a 'Senior Developer' on 'Source 2' at 'Valve Corporation'. He goes on to list that he worked on 'Source 2' at Valve from November 2012 to February 2013, which fits in with the theory that the Source engine has been a continuously evolving and ongoing project.

Of course, Valve have no official comment out as of yet, and Leonard's profile is merely adding to the pile of rumours surrounding this much anticipated next engine upgrade for Valve. Source 2 would be very nice indeed, but with Valve's recent titles such as Portal 2 and Left 4 Dead 2, it's not as if they are lacking in the graphics department. Either way, I'm sure Valve will tell the gaming world when it's ready.