It varies by load, and they confirm in the interview (and I think in the separate DF analysis) that it's sometimes native, though I'd assume barely in the action sequences.
The pipeline is set up so post-effects and some other elements are still done natively after any geometry reconstruction, which is a smart way to keep IQ looking good for the output target, even when the engine is strained.
Keeping the post processing effects at native 4K and 1080p resolution is indeed a smart decision for motion clarity. Must have been costly though.
I was misinformed about the target ceiling, but it's hardly ever native because resolution is always adjusting according to DF.