A recent reddit Valve tour may spill some beans about what's up at the developer, as a photo of a monitor (blown up but blurry on NeoGAF) has emerged allegedly taken during the visit that shows an internal change log showing work progressing on Left 4 Dead 3 and Source Engine 2. This is unconfirmed, but plausible, as Valve has already seemingly confirmed Source 2, and it's not like they are reporting something farfetched like the continuation of the Half-Life series. Thanks Eurogamer.