Improved Ultimate is a passive skill available to all playable characters in RWBY: Grimm Eclipse. It has two levels, Improved Ultimate 1 and Improved Ultimate 2, each of which can be used to unlock 1 extra ultimate bar. Each upgrade costs 1 point to use.
Improved Ultimate 2 must be unlocked by defeating 300 enemies using Ultimate attacks, across all characters. Prior to being unlocked, it is called Specialist.
In Early Access, it was called Improved Special 1 and Improved Special 2 and each gave access to 2 extra special points, but was otherwise the same.