While we can't see much of the phone, which is enclosed as secretly as every engineering prototype from Samsung in the last two years, we can see the display, which is claimed to be with QHD (1440x2560 pixels) of resolution, and a 5.2" size. The other top-shelf specs are rumored to be a next-gen 2.5 GHz Snapdragon 805 processor, 3 GB of RAM, and a 16 MP camera with optical image stabilization. A Samsung phone with such specs already appeared a few times in various benchmarking databases, including last week on GFXBench, so there might be some merit to the speculation. Moreover, the interface language is in Vietnamese, and we know Samsung has a factory there, from which a number of all-telling leaks have appeared in the past.
The thing here is that the speaker grill on the phone enclosed in this angular test mule chassis, is located at the bottom, like on the Note 3, so it might very well be an early version of the Note 4, rather than a representative of Samsung's eventual premium design line. That's in case the leak is credible at all, as there is not much else we can deduct from the pictures below, especially the thing that interests us most - the finalized design.