http://powerupgaming.co.uk/2015/11/06/crystal-dynamics-clarifies-rise-of-the-tomb-raiders-resolution-cutscenes-not-true-1080p/
Gameplay is 1080p.
Game director Brian Horton reached out to Power Up Gaming earlier today to clarify that cutscenes in the game will be rendered at 1440 x 1080, not the 900p we previously reported via gaming outlet Gamersyde. This rather unorthodox resolution offers an eight per cent resolution improvement over 900p, as well as limiting upscaling to the horizontal axis.
Gameplay is 1080p.