The site says 2-4 people in servers. Some people have hacked to support 64 players though.
Well the site is dumb and wrong apparently. I was only today in a server with whopping 5 people. Above 4 aren't supported because you can't see the stats of the extra players.
hope it doesn't go the way of Minecraft's constant releases.
Minecraft is badly developed anyway since it goes into very different directions. Its like someone took 4 random people who were qualified as coders called A, B, C and D, told A to make a game about exploration, B to make a game about building, C to make a game about RPG and D to construct a wall around the office to repel any artistically talented person who offers to make the game look "not like complete ass" and the guy who will explain them that a "final version" means the last update in the game meaning that the neat list of features you wrote down couple of months earlier should be in the game by the time that "final update" goes online.
Also since the game is in Alpha, everything is subject to change. If you complain loudly enough I'm pretty sure the developers (Who happen to be a husband an wife which i think is pretty cute) will fix those problems.
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