https://www.gamespot.com/articles/destiny-2-curse-of-osiris-dlc-release-time-preload/1100-6455330/

Destiny 2's first big expansion, Curse of Osiris, is drawing near. With its release date scheduled for Tuesday, December 5, Bungie has shared some details regarding launch day and pre-loading, and it's also delivered a new trailer highlighting some of the DLC's new content. [Update: Destiny 2 servers are now offline for maintenance and are expected to be back up at 10 AM PT, at which time a new update and Curse of Osiris will be available.]