I removed my post from earlier today about the supposedly-imminent opening of the new DDI at GA 400 and Abernathy Road. In fact, there are mast arms that haven't been installed yet, and some that have been installed don't have bagged signal heads on them.
What did happen over Friday-Saturday night is the temporary diversion of all eastbound traffic to 400-Glenridge and Roswell Road to the one-lane permanent Roswell Road offramp, which, of course, has been striped as two lanes by commandeering the shoulder. I'm a bit surprised that both of the right lanes of 285 are dropped there rather than having an option lane as was done at the previous 400-Glenridge offramp. Doing this moves the point at which the mainline reduces to three lanes a good mile-and-a-half upstream. A member of our Georgia roads Facebook group posted a video of his trip down the new offramp, but I was curious enough about the mainline and the DDI to check it out myself (plus the weather was gorgeous and I wanted to try out my new phone camera!).
The fourth lane is reopened a little before the Roswell Road bridge, which means that traffic from the onramp from Roswell Road still has to merge into it, then move left again to remain on eastbound 285.
Also, in the westbound direction: I'd thought that the onramp from Glenridge to 285 added a permanent fourth lane to the 285 mainline, same as the Peachtree-Dunwoody onramp does eastbound. Either I was wrong, or it's been changed. Now, the combined westbound CD and the Roswell Road onramp add two lanes to the now-three-lane mainline, with the former fourth lane ending upstream somewhere. If someone can clarify that, I'd appreciate it.
EDIT: The reason for this detour is that they're replacing the decks on the bridges over Long Island Drive and Lake Forest Drive. that means that they'll shift traffic to do the rest of the bridges at some point.