The version tested was 22.214.171.124 and motion blur was on for this test. There have been reports of severe performance issues in zombies on Xbox One (https://www.reddit.com/r/Infinitewarf…), but this is not something that I have personally experienced.
Pixel counts indicate that the zombies mode in Infinite Warfare on Xbox One uses a dynamic resolution ranging from 960×1080 to approximately 1390×1080. There also appears to be a temporal technique used that improves the resolution over time for parts of the frame that are similar to previous frames and with this technique pixel counts can reach 1920×1080.
Source: VG Tech