Once you finish Diablo 4's campaign, your main goal is to work your way up the World Tier ranks to earn better loot from harder monsters. Right now, World Tier 4, aka Torment, is the highest level of difficulty, but there's evidence of another tier in the action RPG's files.
Former Diablo Immortal dataminer DatamineARPG has found text and an icon for World Tier 5 that would fit in Diablo 4's existing difficulty menu. The dataminer said they found a marker placeholder that would point to the capstone dungeon you would need to finish before you unlock it.
