Apple has released new builds of iOS 12.1 beta to support the latest iPhone XS and XS Max, including the delayed Group FaceTime feature.
The first beta of iOS 12.1 was released earlier this week for existing iPhones, but now that the iPhone XS and XS Max are available to customers, additional builds have been released.
This comes at the perfect time for customers who like to receive new iPhones today, because it is impossible to restore a new phone from a back-up of a newer version of iOS. So if a user's current iPhone had iOS 12.1 beta, there is no way to restore a backup of that device so that that version of the operating system runs until the new iPhone XS or iPhone XS Max is also updated to the beta.
The iOS 12.1 beta seems to be a minor update so far, usually with support for Group FaceTime. Other minor changes were found in the code that is probably intended for the new iPads that will land this fall, such as horizontal Face ID support.