You can switch to the beta branch on Steam:
Right click on the game -> Properties -> Game versions -> Beta
You can only play with players using the Beta branch if you are playing on the Beta branch
Beta branch quick fixes:
People can't leaving the first mission should be solved
The QUICK HOST button now creates a private lobby, so other people can't join and break things up
WASD Keybindings added
Opened every map to be playable because of the first bug (which could lead to not finishing first mission and not opening the other levels)
Removed fps drops when players shoot?