According the Crossout Facebook page, fans looking to see what a vehicular MMO is like can get signed up during this week's "mass recruitment event". Those who have already registered to participate will get guaranteed access and those who sign up between now and February 7th will have a "significantly increased" chance to be chosen.
At this stage of the Crossout Battle test, players awaiting new parts of armoured vehicles, an improved crafting system and the recently added faction system. First factions: Scavengers, Traders, Lunatics and Engineers - will give players access to factions vehicles, rare vehicle parts, access to the new missions and a variety of bonuses depending of the player's reputation within the faction.
You can sign up on the Crossout page.