The Marines decided they want to phase out the HMMWV with a replacement that has the same versatility, but is more survivable, quieter, and less of a gas hog.
Technically the Shadow is a concept vehicle, but it's further along in development than any of the other alternatives, so it seems like a realistic option.
Reserve units will definitely still have the HMMWV, and the Air Force isn't looking at any replacements.