Google will no longer offer Hangouts on Air.
Hangouts on Air will be replaced by YouTube Live. YouTube Live will let you create public, private, and unlisted broadcasts. Broadcasts will be automatically stored in your YouTube account. The most significant change for many users will be the removal of the Q&A feature that was in Google Hangouts on Air. Now to host a Q&A you will have to share Google Slides and use the Q&A feature integrated into the presenter mode in Google Slides.
Just to clarify, there will still be a video chat feature in Google+, this change only applies to Google+ Hangouts on Air.
H/T to The Next Web.