The video chat application was introduced by Steve Jobs at WWDC 10 on June 7, 2010.
Apple released the new betas just yesterday, but without the group chat function for Facetime. As the company announced, this has been removed and will not be included in the final version of iOS 12 and macOS Mojave. No reason was given for this step, but it can be assumed that the function has not yet been completed.
What can “Group Facetime” do?
With Group Facetime, up to 32 users can chat on Facetime at the same time. Thanks to augmented reality, it is possible to appear as an “Animoji” during the video chat.

Due to Apple's cancellation, users now have to be patient. The iGroup wants to deliver the function in a later update in the fall. Since Apple likes to postpone updates, it could take longer under certain circumstances.