The documentation says ten people can be in a Hangout but I'm hearing that Hangout video maxes out at six people.
Which is correct?
For the desktop environment:
Specifications for sending and receiving messages
You can have a group Hangout with up to 100 people.
Requirements and specifications for video calls
Video calls can have a maximum of 10 participants.
Sometimes you want to have a Hangout with multiple people at once, like when you're planning a trip with several friends or choosing a convenient meeting time. With Hangouts, you can have a discussion with up to 100 people and have a video call with up to 10 people.
Hangouts video calls are limited to 10 video conference participants, with no time limit. You can also use Hangouts On Air to broadcast a Hangout to many more people, though there is still a limit of 10 active participants.
If you activate Google+ premium features, the limit increases to 15 participants for both Hangouts video calls and Hangouts On Air. The limit remains at 10, however, for Hangouts created from the Google+ Events page.
The new video calls limit for Google Apps for Work (Work, Gov and Edu) is now 25. "Hold video calls with up to 25 participants."
See the following article under "Google Apps editions" https://support.google.com/a/answer/6065029?hl=en
Google announced this new limit on 3/16/2016 via the blog: http://googleappsupdates.blogspot.com/2016/03/connect-with-more-people-using-google.html
You can now have 150 people in a standard text hangout, and video calls can have 25 participants.
Now 2016, Google Hangout support maximum 25 concurrent users (enterprise/education version). If you use Hangout on Air, everybody can watch with no limit.
It seems that Hangouts supports up to 10 people call on a free account:
You can add up to 9 people in a Hangouts video call (Source)