Halo is moving to Unreal Engine 5. Here’s the topline from 343 but…not 343, as along with this announcement is a rebrand to “Halo Studios”:

Unreal Engine 5 has been revolutionising game design, and we've just seen a new, and unexpected example. 343 Industries, now renamed as Halo Studios, has announced that it's moving from its proprietary engine Slipspace to Unreal to work on multiple new Halo games.

Members of the newly-renamed Halo Studios explain why they are switching from the proprietary Slipspace Engine to Epic's Unreal Engine 5.