Euro Truck Simulator 2 and American Truck Simulator get official multiplayer support and the open experimental beta for both is now available. The multiplayer comes in the form of a Convoy mode, which allows eight players to drive together in the same world: AI traffic, time and time are synchronized and all eight players can be in the same job.
Both games already have modifications that add multiplayer, but it’s good news to incorporate the functionality into the game, though so far, it’s not as flexible as some community-based features.
Because it is an experimental open beta, there are currently limitations. Modifications are not yet compatible with multiplayer, and everyone must share the same DLC as the host. There are more things to keep in mind, explained in detail here, but rest assured that you have the option to return to a previous saved game state when you exit multiplayer.
Instructions on how to enter the experimental beta version 1.41 update they are here. There's no word yet when the update will be out of beta, but in the meantime SCS is after your comments.