Multiplayer
From Space Engineers Wiki
Multiplayer has been confirmed for Space Engineers. Personal servers is being looked at with players hosting their own world/sector to the public or have it private. Servers can be dedicated or non-dedicated with a browser list supporting Steam match making. Players should be given as much freedom as possible when it comes to hosting their own worlds. [1]
In addition to this, worlds will be persistent and can be loaded from save files at the server admins discretion.[2]
Lan support is also in the works.[3]