The title should say everything in a news story, and this one's no stranger to that adage. Also something that's not a stranger to something else, is Valve's generosity to just about anyone who shows up on their doorstep– granting studio tours to regular people like you and me, and Chet Falizek.
You don't care. All you want to know is where's the proof.
It just so happened that a group of people visiting for the DOTA 2 International something-or-other were treated to a tour of the company, where one of the pictures snapped by a guest seem to innocently reveal direct references to both the Source 2 engine, and Half-Life 3:
Just kidding, it's Left 4 Dead 3– according to Ted Carson, if that is someone's real name.
Still paying attention? The original images showed up in the DOTA 2 subreddit, which prompted a more official post on the Gaming page, and a thread on the NeoGAF forum you can find on the upper right corner of this website. The sliver above comes from the incriminating selection of a monitor on someone's desk.
Now you know something you've already read on Twitter and every other website at least four times this morning.
What you didn't know is that you also already knew Valve has been working on Source 2 for a while, amongst other things, and that Half-Life 3 is never coming out. Whether or not this breach is the advent of a Source 2 reveal on the horizon, or the end of Valve allowing harmless outsiders into their highly secretive studio has yet to be determined. The big takeaway is that the joke about Valve not being able to count to 3 is finally not true, according to Ted Carson.
Stay tuned for baseless speculation of all kinds on the internet this week.