From DownSights: “Season 2 brought a bunch of new Zombies content to Call of Duty: Black Ops Cold War, and even unleashed the undead hordes on the standalone battle royale mode, Warzone.

However, the main changes alongside Outbreak affect the upgrade system in every Zombies match you’ll play from now on.

Teased in the original content reveal of Season 2, now that the update is live we have full intel about the new Refined and Flawless Aetherium Crystals that Requiem agents can collect when fighting against the undead, as well as the new Tier IV and V upgrades that can be unlocked with them.”

Source: N4G PC Black Ops Cold War Zombies Meta Upgrades (Aetherium Crystals) Guide