Blizzard says that instead of any sort of loot box mechanics in Diablo 4, they will instead embrace the Season Pass system. This makes a lot of sense seeing as how Blizzard also announced the removal of loot boxes from Overwatch and Overwatch 2 earlier this month.
Blizzard made this announcement as part of its latest development update. They also confirmed that Diablo 4 will be a full-priced title, so while you are free to spend money on cosmetics if you want to, there will be no way to "pay for power."
After Diablo 4's release, Blizzard says that content will be doled out through Seasons. These Seasons will rotate every three months with each new season acting as a "fresh start" for players. It's similar to what Blizzard did with Diablo 3. You can, if you want, engage in each Season where you will be able to earn free rewards by completing challenges through gameplay. These Seasonal challenges and rewards will be in addition to the Season Passes.
Each Season Pass will include both free unlocks and premium tiers. Each pass will let players earn a variety of cosmetics and premium currency. This premium currency can be used in the in-game shop that will include even more cosmetic customization options. Blizzard does note that "the best looking cosmetics aren't exclusive to the shop." Blizzard also re-re-iterated that "nothing offered in the shop grants a direct or indirect gameplay advantage."
