I have previously discussed the Ultimax 100 Mk4. This is the latest iteration of the Ultimax 100 design and is being entered into the IAR competition by General Dynamics, although it designed by Singapore Technologies Kinetics (STK).
Photos by SMGLee. Click to expand:
Compared to the Mk4 the Mk5 takes unmodified STANAG (M16) magazine, has quad rails and a bipod/foregrip rather than a separate bipod and foregrip.
I am not sure if the Ultimax 100 Mk4 100 round drum magazine will be made compatible with the Mk5. The Mk4 took modified STANAG magazines.
UPDATE: Defense Review has more info.