The update downtime will happen overnight between 1:00-3:00 AM PDT. Once that’s all set, the new Battle Pass: Inner Light, opens up a new season on September 1st. Once the season is live, you'll be able to earn up to 40 ranks of challenges and rewards, with more goodies available from both paid versions. These additional items include the Inner Light weapon and armor cosmetics, an avatar frame, a rank boost, depending on which pass you buy.
As for the new Helliquary boss, well it’s bosses, since there are two new demonic bosses to challenge. Gishtur and Beledwe count together as the fourth boss added, so you’ll get to take them on starting on September 2nd.
“Beledwe prefers a flame-infused trident, using it to call down meteor strikes and summon burning orbs that seek you out. Gishtur goes for a more close-quarters approach, sporting a massive, spiked sword and entering a frenzied whirlwind to close any gap. Be cautious, as they’re known to incinerate opponents’ side-by-side.”
If you manage to claim victory, you’ll get an item from their remains, Twin Horns, which gives a 10% skill cooldown reduction when you’re inside Challenge Rifts.
In quality of life changes, the Legendary Gem tooltips get a lock button to prevent you from accidentally consuming a gem instead of upgrading it as intended.
The events slate for the next few weeks looks to offer some challenges in September. The first event, Hungering Moon, runs from September 9-12th and you’ll have to fulfill demands from the moon for rewards. The Scorched Sea runs from September 14-28th, with daily tasks to complete for rewards and milestone rewards with enough tasks completed.
Finally, Mists of Cyrangar will happen from September 21-30th, and also bring daily tasks and horrors to fight. This comes with a special challenge. With completed tasks, the mist on the event page clears a bit, and when it’s clear, reveals a hint about the first major update. To prepare for that update, they're trying to get as many players as possible up to Server Paragon level so there will be a bonus experience buff for all players who haven't reached that level yet running during the event (or until you reach Paragon).
For the complete announcement, head to Diablo Immortal.