Halo 4 rejected map pitches
During the development of Halo 4, company Digital Extremes was contracted by 343 Industries to help with the production of the game's DLC map packs. A number of map ideas and concepts were pitched to 343 but went unused, and have since been released online.
Known map concepts
Covenant underwater technology
Identified in a series of concept art uploads all titled
Last Resort remake
One map concept shown involves a paintover of the sniper tower area of the Halo 3 map Last Resort. Its filename,
Other DLC map concepts
Some callout sheets for individual map props have been posted online, of which tie to no particular known map.