You’ll get all the expansions, including Beyond Light, but Season Passes must be purchased separately.
Bungie had a fairly interesting presence at the Xbox Games Showcase, showcasing the new Stasis abilities coming with Destiny 2: Beyond Light. It also confirmed that Destiny 2 and all of its expansions would be coming to Xbox Game Pass. This includes Beyond Light and should be a nice way for new players to be introduced to the world (despite all the content that’s being vaulted).
That being said, seasonal content will not be available for Game Pass subscribers. Bungie clarified this recently, stating that, “With an active Xbox Game Pass subscription, players will have access to the standard edition of the Forsaken and Shadowkeep expansions beginning in September 2020, and the standard edition of the Beyond Light expansion beginning on November 10, 2020. Seasonal content is available for separate purchase.” This means that new events and loot, along with Season Pass ranks, will not be accessible for Game Pass players.
Destiny 2 is a free to play experience so you’re really paying for access to the expansions on Game Pass. If said expansions leave the service, then you’ll need to purchase them separately later. Also, bonuses from pre-ordering Beyond Light will not be on the service – you’ll still need to purchase the upcoming expansion to receive them.
Destiny 2: Beyond Light is out on November 10th for Xbox One, PS4, PC, PS5 and Xbox Series X. Stay tuned for more details in the coming weeks.