https://www.gamespot.com/articles/destiny-2-forsaken-ps4-xbox-one-pc-release-date-pr/1100-6459410/

Destiny 2: Forsaken is the online shooter's big year-two expansion. It launches on September 4 for Xbox One, PS4, and PC. Just like The Taken King for the original Destiny, Forsaken is a major new piece of content that 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 following 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 overall goal is to give players more reasons to keep playing once they reach the endgame.