It's out, and downloadable here. The Core rulebook, bestiary, and module Doomsday Dawn are all there for free. Print versions are also showing up at your FLGS and online, and no doubt it's the talk of the town at GenCon.
I have a print copy of the rulebook, and so far it's an interesting dive into yet another alternate reality where Pathfinder morphed into a mythical alt 4E and now a mythical alt 5E. As I digest it, more discussion to come.
EDIT: I'll say this much, the new monster statblock is even tighter and more compressed than the Starfinder or Beginner Box statblocks.
EDIT #2: Why do all orcs now and forever more have to be cursed with getting back up after they should be dying? Thanks, 3.0!