Valve has just pushed an update for Dota 2 on the Steam service that adds some peculiar new text files that reference Half-Life 3, as well as some role-playing game mechanics, not to mention a few features relating to its virtual reality efforts.
Half-Life 3 has become a true vaporware title in the last few years, as Valve isn't willing to share anything concrete about its long-awaited title, preferring to focus on other things like Dota 2, Counter-Strike: Global Offensive, or its virtual reality partnership with HTC for the Vive headset.
New Half-Life 3 mentions appear in a Dota 2 update
However, it seems that some progress is being made. SteamDB confirms that three new files have just been added to Dota 2 in a new update and, according to the dissection on ValveTime, they contain a lot of new references, possibly to Half-Life 3.
First up, there's the hl3.txt file with includes old references to previous games but also some new aspects, like the mention of role-playing game mechanics like a quest system, non-playable characters, and more. The NPCs are also described in relation to the Combine, the enemy faction in Half-Life 2.
There are also mentions of some virtual reality aspects, like the Chaperone system, a movement system, as well as ziplines, although it's unclear how they all factor in a new game.
Half-Life 3 may have or might have had RPG mechanics
There's also a new rpg.txt file that contains definitions for role-playing game elements for the Source 2 engine. The actual references aren't tied to any specific game so it's unclear if Half-Life 3 will go full on RPG shooter, like Fallout 4, for example.
Last but not least, a lights.txt file contains definitions for lighting systems but also an all-new "Realistic Day/Night cycle" that contains extra settings and adjustment capabilities.
It's possible that Valve accidentally added these files to the latest Dota 2 update but it's also possible that these were left over from the global Source 2 engine development and come from other projects based on the technology, hopefully an actual Half-Life 3.
Valve hasn't commented on the leaked files.