“The Age of Hatred kicked off with the launch of Diablo IV and Lilith’s resurrection and was protracted by Mephisto’s resurgence in Vessel of Hatred.
Throughout 2025, you will experience the spread of Mephisto’s influence through new seasonal themes and questlines”

“In addition to new Seasonal content and permanent game additions, you’ll see on the Roadmap that we are bringing 2 IP collaborations into Diablo IV this year.
We can’t shed light on them currently, but we’re extremely excited to meld the Diablo universe with universes that complement its dark themes.”

Source: Blizzard