http://www.ign.com/articles/2014/10/07/kingdom-hearts-3-switches-to-unreal-engine-4
Kingdom Hearts III is now being developed with Epic Games' Unreal Engine 4, according to director Tetsuya Nomura.
The developer told Famitsu (via NeoGAF) that the change was made for "various reasons" and, despite initial teething issues, no further slowdown is expected as a result of the switch. Epic is apparently assisting with any problems encountered.
Up until this point it's believed the third installment in the Kingdom Hearts trilogy was being developed using the company's Luminous Engine, which was unveiled at E3 2012 through the Agni's Philosophy tech demo. While Luminous is still believed to be in use for Final Fantasy XV, it's unclear if any other projects are still making use of it at this time.
A demo of Final Fantasy XV will be included in launch copies of Final Fantasy Type-0 when it launches in early 2015. In other news out of last month's Tokyo Game Show, an impressive new trailer for the game was revealed alongside news director Tetsuya Nomura left the project in order to focus on Kingdom Hearts III.