The new update of Google Hangout will prompt the YouTube Live, Google's other live video product, to broadcast in real-time.
Google support document states users can set up the new Hangouts On Air by creating either a "Quick event" or a "Custom event" using YouTube Live's Creator Studio tool. You can either go live immediately or schedule a YouTube Live broadcast for later.
As with the version on Google+, you can have the Hangout be public, unlisted or private to just a select group of invited guests. The only major change would be losing access to features such as Showcase, Applause, and Q&A, though they might be in the future.
The move to YouTube is yet another sign that the company is moving away from Google+. Last year, it moved Google Photos to its own product and even completely redesigned Google+ to be more of a community site than a social network. It also retired the G+ account as a requirement to register for services like Google Play Games and YouTube.
This is yet another feature getting pulled out of Google+, following Photos last year. Perhaps, though, this move makes sense. Recorded broadcasts from Hangouts On Air were archived in YouTube anyway, so consolidating the broadcasting platform and the archive location seems like a smart move.