There are a lot of unanswered tweets asking for clarification. Given the game's performance at 1080p I won't be terribly surprised if it turns out to be more complicated than just "native." 4K checkerboarded would make it "native" in the sense that it isn't being upscaled after temporal reconstruction, unlike some games which use checkerboarding to reach ~1800p and then get upscaled from there to 4K. On the other hand it isn't "native" in the sense that only half of the pixels are going through a traditional rendering pipeline for each frame. Or it could be "native" in the sense that geometric resolution is 4K but shaded resolution is still 1080p using MSAA techniques like some other titles.
This is going to be a complicated generation in this respect. Lots of work for Digital Foundry to try to detect the specific techniques being used, as I don't expect marketing to give us the straight story in most cases. That means we won't really know until the hardware and software has been in the wild for a bit.
