The studio noted that the transition would happen back in January, when it announced that it was separating from publisher Activision Blizzard to be the sole company in charge of Destiny. Battle.net is a PC games launcher created by Blizzard. It mostly hosts Blizzard games but does include a couple from other Activision studios, notably Call of Duty: Black Ops 4 and Destiny 2.
Now that Activision Blizzard will have nothing to do with Destiny 2, Steam makes sense as a more neutral home for the online shooter. October 1 is also the day that Destiny 2 will launch its free-to-play version, New Light, and new expansion, Shadowkeep. It’ll be a busy day for Bungie.
PC players can do a one-time transfer to carry over all of their characters and progress from Battle.net to Steam. Aside from starting the game from a new launcher, the experience should be the same.