With the introduction of Amirdrassil in Dragonflight Patch 10.2, Great Vault thresholds have also changed! Unlocking raid reward choices now requires 2, 5, or 7 boss victories, as opposed to 3, 5, or 7 in Aberrus, making it slightly easier to earn the first vault reward.
The current vault requires 3/5/7 Aberrus raid bosses, while Patch 10.2 will be reduced to 2/5/7 from Amirdrassil.