Inside the editor on the Collaborators menu (and also on the animation details page, via clicking the 3 dots on an animation in the gallery), you'll now see a switch to have people join via URL. You can copy the link with the token and other users can just join and leave, it will not take up the traditional "collaborator slots" when people join this way, but you're still limited to 4 simultaneous editors. This is useful for having many people take part in a larger collaboration!