https://www.gamespot.com/articles/destiny-2-forsaken-release-date-pre-order-guide/1100-6459410/

Developer Bungie has finally revealed Destiny 2's big year-two expansion. It's called Forsaken, and it launches on September 4. Just like The Taken King for the original Destiny, Forsaken is a standalone expansion you'll have to buy separately even if you purchased Destiny 2's expansion pass. In fact, you can even buy a new "annual pass" to pre-order three additional content releases that will come out after Destiny 2: Forsaken.

Forsaken's story will bring players back to the Reef to fight off a group of powerful enemies who broke out of prison. The expansion also introduces a number of changes to Destiny 2, including a new mode called Gambit, as well as major changes to weapons, mods, and Masterworks. The idea is to keep players coming back once they've reached the endgame.