Diablo IV’s next seasonal chapter, Season of Hell’s Legacy (Season 15 / patch 3.2.1), begins rolling out on September 15, 2026 at about 9:30 a.m. PT — Eastern calendar day September 15, roughly 12:30 p.m. ET if you convert the Pacific rollout stamp. Blizzard’s season overview frames it as the centerpiece of Diablo’s 30th anniversary celebration: stay awhile, listen, and hunt memories of Sanctuary’s darkest hits. Primary details are in Blizzard News.
The seasonal questline brings back the lost soul of legendary Horadrim Deckard Cain amid rising dead from Pandemonium. Players confront dark wanderers and enter nightmares of their past, collecting three Splinters of Evil by defeating echoes of Diablo beneath Tristram Cathedral, Baal at Arreat Summit, and Mephisto within the Durance of Hate. You bear one Splinter at a time — unlocking Fire, Cold, or Physical Iconic Powers and matching War Plans reputation tracks — and can swap Splinters by clearing the largest Waking Nightmares.
Waking Nightmares recreate Diablo history in three flavors: multi-level Capstone-style Prime Evil showdowns, standard-length fixed dungeons (think familiar moments rebuilt for Diablo IV), and sudden open-world one-room pop-ins with past bosses or monster waves. Separately, Soul Splinters act as season gems tied to demonic powers and artifacts, while shared War Plans reputation now carries across matching account partitions (Eternal/Seasonal × Hardcore/non-Hardcore × Normal/Solo Self-Found), with Season 14 progress carrying into Eternal at the September 15 changeover under Blizzard’s living-Hardcore caveat.
Rebirth lets you convert an Eternal character into Seasonal play by resetting to level 1 while keeping class, name, appearance, and Hardcore/Normal state (stash gear first; retained inventory is wiped on Rebirth). Legacy Uniques inspired by classic relics also land as permanent Seasonal/Eternal additions. On the promo side, Blizzard’s Diablo IV × The Witcher 3 note is a crossover cosmetic: a Geralt-themed skin in Diablo IV for Battle.net Songs of the Past pre-purchase or post-launch purchase — not a Witcher ship and not a Diablo expansion.
Keep the beat map clean: an Amazon class pack headed to Diablo IV in the first half of 2027 is a separate What’s Next / slate item, not a Season of Hell’s Legacy feature. Switch 2 Age of Hatred Collection street timing on the same calendar day is a different SKU story and is not this season systems lead. For adjacent live Diablo franchise coverage already on RCG, see Diablo V Locks Spring 2029 as Sanctuary Falls — different game, useful slate context only.
Platforms for Diablo IV remain PC, Xbox, and PlayStation for this season rollout. Until Blizzard publishes a tighter end date or additional first-party hours, the accurate US desk line is Season of Hell’s Legacy starting September 15, 2026 (~9:30 a.m. PT), Cain questline, Prime Evil echoes and Splinters, Waking Nightmares, Rebirth, shared War Plans, and the Witcher Geralt Battle.net promo skin.
What we are not saying: no Amazon-as-season-feature claim, no physical Switch SKU invented for this season piece, no merge with Diablo V Spring 2029, and no treating the Geralt skin as a Witcher 3 release.
