For much of the game, PS4 resolves at around 1000p, and Xbox One around 810-828p. Gaining absolutely accurate metrics is difficult owing to the temporal super-sampling anti-aliasing, which makes it very difficult to find the hard geometric edges essential for pixel-counting.
However, the Titanfall 2 beta dropped frames hard on both systems, so yes, resolution will drop below the beta's fixed framebuffer standard - we've seen PS4 drop to 720p in the most intense of scenes, while Xbox One will fare worse. We've yet to determine how low it drops - temporal reconstruction is really difficult to work with, but it can look bad. We've actually recorded edges that range from 480p upwards - however, Titanfall 2's post-process pipeline may be working with lower resolution alpha effects, reducing pixel count where transparencies intersect with geometric edges.