The Haunted Mansion Holiday also re-opened a few days ago. This is the earliest I've ever seen the transition made, being advertised as "reopening ahead of the Halloween season".
Interestingly, Disney states it's "only available via a Virtual Queue", where visitors use the Disney app and join a queue through it, making sure they're using their MyDisney account and that their park tickets are connected. There's two daily opportunities to join it: at 7 AM and 12 PM.
Hopefully this virtual queue thing is temporary, as I've seen people saying the HMH still looks to be under construction. They may just be using it for early access at the moment, as it says on the Disneyland site:
"Even though New Orleans Square is currently being refurbished, you’ll be able to socialize with Santa Jack again soon when Haunted Mansion Holiday reopens—available via our virtual queue only, as our new stand-by queue experience hasn’t quite materialized yet. Using a virtual queue allows us to welcome back foolish mortals to this eerie estate once again, while we continue work on the surrounding area."