Announced in February 1997, N64.com (IGN) wrote the following...

Ultra Descent, based on the Descent series originally launched on the PC in 1995, is Interplay's third title in development, and is likely to arrive before winter holiday 1997. Although the game is still not confirmed by Interplay, it's likely Parallax or Interplay developers will go to work creating completely new levels special to the N64 version. Interplay could not comment on whether the game would feature multiplayer capabilities.

Original source: ign64.ign.com