Bungie has taken Destiny 2 offline in the wake of its shift to Steam (which can be pre-loaded now) and going free-to-play. Maintenance is currently ongoing and should end at 10 AM PT/1 PM ET. However, at that time, update 2.6.0.1 will be rolled out for Destiny 2 and should be done by 12 PM PT.
So if you experience some issues signing in fro 10 AM to 12 PM PT, this will be due to “background maintenance”. Regardless, it’s a brave new age for Destiny 2. Along with the launch of Destiny 2: New Light, Bungie is also releasing a new expansion called Shadowkeep.
Furthermore, players who were previously on Battle.net can shift their profiles over to Steam. If you enabled cross-save for Xbox One and PS4, then those characters can also be transferred to Steam once New Light is live. It might take some time before Forsaken owners see their licenses for the game show up though.
Pinnacle weapons are going away and power progression is also being overhauled so be prepared. Head here to see what content will be available free for New Light.