
Legendary powers are Unique Equipped: one cannot gain the same power both from the Cube and from an equipped item. Seasonal characters roll over their collection when merging at Season's end. Power collection is shared among all characters of the same type on account. There is no level requirement items do not need to be level 70. Extracting power from an item destroys the item. During Season 22, Kanai's Cube received a 4th slot that can be filled with any power normally allowed in the other three, but a duplicate power will not stack. One effect from a piece of jewelry ( rings or amulets). One effect from any other piece of armor ( boots, pants, helms / spirit stones / voodoo masks / wizard hats, pauldrons, bracers, chest armor / cloaks, gloves, or belts / mighty belts). One effect from either a weapon ( one-handed or two-handed) or an off-hand item ( quivers, mojos, sources, phylacteries or shields / crusader shields). While characters may only have up to 3 of them active, they can store all acquired essences within the cube, swapping them at any time when in town without losing essences they override.
The extracted abilities are stored within the Kanai's Cube, and are not lost if replaced. They are extracted via a recipe known as Archive of Tal Rasha.
Kanai's Cube powers are passive abilities extracted from various legendary and set items in Diablo III: Reaper of Souls.