Twitch is getting new Group Chat functionality that will allow users to create and participate in invite-only chat rooms "that live separately from the traditional Channel Chat." Since it's currently in beta testing, creation of these invite-only rooms are limited to members of the Twitch Partner Program; however, any Twitch user can be invited to join a Group Chat room.
"The beta period is necessary to ensure that Group Chat is stable and scalable before we roll out room creation to everyone," explained Twitch's VP of Marketing and Communications Matthew DiPietro. "We’re always working hard on stability and shoring up the QoS of our chat service in general, and we are keen to roll out this new feature to the rest of the community as quickly as we can."
Group Chat rooms currently don't have a limit for the number of people who can be invited, but Twitch will monitor the parameter and assess it during the beta period. Users will be able to join up to 10 Group Chat rooms at a time.
At this point, the full rollout for Group Chat is still to be determined, but Twitch is working "very hard" to get the feature out to the global user-base. Group Chat rooms, at least at launch, will only be supported on the web portion of Twitch, but hopefully there are some plans to introduce the feature to consoles and mobile devices in the future. You can check out the full Group Chat FAQ here.