Twitch began beta testing a new feature called Subscriber Streams today that will enable eligible streamers "to offer exclusive streaming content to subscribers." The streams will only be viewable by a channel's subscribers (at any tier), while everyone else will be shown a preview and invited to sign up.
In order to broadcast a Subscriber Stream, streamers must be a Twitch affiliate or partner for at least 90 days, and have a clean record for the previous 90 "unique broadcast days," meaning that if the channel eats a suspension for any reason, the counter starts over.
"As with any other stream on Twitch, Subscriber Stream content must fall under our Terms of Service and Community Guidelines," Twitch warned. Subscriber Streams will be tagged as such "for easy discoverability," Twitch explained. The tag will always appear first, and cannot be removed.
Post-stream VODs will be available to subscribers automatically, and further permissions can be edited through the Video Producer tab on the dashboard. Clips created from Subscriber Streams will not be restricted in any way, so if you want to keep those under control you'll have to make use of the Clips Manager moderation options.
Twitch also emphasized that while Subscriber Streams are intended to be more intimate affairs, they are not private streams, and Subscriber Stream privileges can be revoked if you get caught streaming, you know, private stuff.
"They are smaller, more personal broadcasts that are available only to your subscribers, Moderators, and VIPs," it explained. "Whether or not your content is being broadcast to everyone or just your core supporters, the rules are the same. All content must follow Twitch’s Terms of Service and Community Guidelines. Subscriber Streams are not a free pass to avoid those rules and guidelines."
As for what unfulfilled need Subscriber Streams will address, that's a little less clear. Aside from the streamer requirements and mandatory tagging, Twitch said they're "pretty much the same as any other stream ," but possibly with the potential for a more personal degree of interaction with subscribers: "We could definitely see competitive streamers taking requests on heroes or champions to play, tabletop streamers running a weekly campaign for Subs, music streamers making all-request set lists, and a whole lot more."
A more detailed rundown of Subscriber Streams, including an FAQ for content creators, is available on the Twitch help site.