Hidden in Valve's Source Filmmaker are files that point to a next generation Source 2 engine, perhaps providing a reasonable explanation for why the company has yet to produce Half-Life 3.
Valvetime.net uncovered files that carry several lines of code reference to ‘Source 2', suggesting the studio is working on a totally new engine for use in future titles.
"Return an str with the current engine version. If key doesn't doesn't exist, assume 'Source', otherwise invalid—assume next-gen 'Source 2'," one bit reads.
"We don't like to brag, but Source is considered the most flexible, comprehensive, and powerful game development environment out there, and it's about to get even better."
The development of a new engine would certainly provide reasonable explanation for Valve's perpetual silence on the much-demanded Half-Life 3.
No word from Valve on the matter, so consider this unconfirmed info for now. With that in mind, it's hard to deny that something big appears to be in the works here.