Valve just announced that the Steam Stealth Fest will run from July 24 through July 31. This Fest, like all the ones that came before it, will include discounts, demos, and more all focused on games that have some measure of stealth included.
As with the thousand (give or take) previous Steam Fests that have occurred, this one comes with a preview trailer to give a sample of what's to come.
The Steam Stealth Fest begins on July 24th at 10AM (PT). It can be found under the Stealth section on Steam once the event goes live.
That said, Kaci is definitely more "all-in" when it comes to the announcements. Valve typically had a very low-key approach to announcements prior to her joining the team. She brings a great deal of energy (and comedy) to the announcements and she's crushing it.
Meanwhile I completely ignore the fact that you have screenshots of pre-retail Left 4 Dead that nobody else has. Not those angles anyway. The deliciousness takes priority! (Good on you Doug! Hope you're having fun with whatever you're doing now.)