The upcoming 2.3.0 patch for Diablo 3 will make some big alterations to the game, including the addition of a new zone, updates to the crafting system and adventure mode, new difficulty levels, and Kanai's Cube, a powerful artifact that spawned the Horadric Cube from Diablo 2.
Kanai's Cube is apparently found in the lost Tomb of King Kanai, one of the locations in the "frozen wasteland" of the Ruins of Sescheron, the upcoming new zone, which will also shine light on some "new mysteries from the lore of the mighty Barbarians." The Cube can break down Legendary items, enabling players to equip their special effects as passive skills (separate from their regular passives), converts crafting materials from one type to another, and does "so much more."
The update will also remove the Realm of Trials, a change that first came to light back in April, and improve Bounty rewards "by adding new Act-specific crafting mats to Horadric Caches." I have no idea what that means, but completing Bonus Acts in Adventure mode will now grant a bonus Horadric Cache with crafting materials, gold, and Act-specific crafting mats.
The new difficulty levels will let high-level players take the game all the way to Torment X, and there's also a new Season Journey feature that tracks individual player progress through Chapters and, for more advanced players, Tiers that unlock new portrait frame rewards and challenges. There are also new Legendary and Set items, and various changes to combat balance.
It's a big update by any measure, and while there's still no release date, Blizzard said its appearance on the Public Test Realm is "right around the corner." Get all the details at Battle.net.