Following months of alleged hints, leaks, and hidden code, Valve has put a full-stop to Half Life 3 speculation with a post declaring it is in no way responsible for the recent teases, and that any rumors of the sequel's existence are the work of wishful fans alone.
“You are being trolled,” wrote Valve's Chet Faliszek. “There is no ARG. Wheatley’s speech was set in Portal 2 fiction – that is all. There has been no directive from Gabe to leak anything. That is all false. I just want to say this so there is no confusion. This is the community trolling the community nothing more. While it is nice to see people excited about anything HL, I hate seeing people be trolled like this.”
Rumors of a Valve-sanctioned Half Life 3 ARG started after a (sadly) unused Spike VGA acceptance video starring Portal 2's Wheatley surfaced with what appeared to be Half Life 3 related code in the background. Valve was quick to deny the existence of any such ARG to LambdaGeneration, but this did not stop the more fevered Half Life 3 conspiracy theorists from spreading word of the impending sequel.
Prior to the ARG rumors, fans were also teased with images of a Half Life 3 shirt worn in public, as well as suspicious code in the DOTA 2 beta and potential plot details found buried in an earlier Portal 2 ARG. While Faliszek's post didn't outright address these pieces of “evidence”, the message made clear that Valve chief Gabe Newell has not done anything official to herald the arrival of Half Life 3.
Or maybe that's what they want us to think...