In the latest iOS 12.1 beta, it has been spotted that there is support for landscape mode for Face ID. Now some might be thinking that this might be for the iPhones, but as developer Steve Troughton-Smith noted, it would require Apple to physically realign the sensors on the iPhones which means that we can pretty much rule that out.
Instead it seems that Face ID in landscape mode would most likely be for the new iPads, especially when you consider that the iPads are generally used in landscape mode since it offers a wider surface area for watching videos, browsing the web, drawing, and so on. Apple has yet to announce its new iPads and many had initially expected them to be announced at the iPhone event last week.
Clearly that did not happen which means that Apple will most likely announce them next month, as Apple has been known to announce products around that time of the year on occasion.