https://www.youtube.com/watch?v=w25fuyEE7g4#t=6698
shows hordes. The dev spawned it, but its going to show you the possibility of what a horde will look like in the game. Zombies are still wonky though, after all it is pre alpha. In the video he spawned 175 zombies at once.
This is just the whole embeded thing the zombie horde spawning starts at like 1:51:32