It's out
https://www.sidefx.com/download/
The installer is the same for the commercial versions and the free Apprentice edition.
New builds are posted every day or two containing bug fixes:
https://www.sidefx.com/download/daily-builds/
https://www.sidefx.com/changelog/
Houdini 15.5 worked fine.
Houdini 16 worked for a couple minutes, then crashed. Now it crashes whenever starting up. Gonna wait for a few builds.