The speculation is over and congratulations to GW for pulling a genuine short-term surprise on the community! You've got to see these things!
Images via 40K Radio
Now that is a Knight!
So WOW! That thing looks to be roughly the size of the Wraithknight, but substantially more bulky. The kit is dripping with detail, especially in the torso-reactor area. There are a lot of levels of plating and inner workings in there. We've seen multiple heads, and at least one other weapon. I have to say if this kit is the anchor unit in a super-heavy based codex - it will shake the game to it's core. These things are going to fly off shelves for both players and modelers alike. And we thought Grey Knights were the low model count army - heh!
~So who's in for THAT!!!