I have never been fan of new hangout that replace the good old Gtalk. I miss the good ol Gtalk days.
Even worse the hangout chat history started coming in my inbox, here is how you can hide it
- Go to gmail Settings->Filters
- Create filter for “Has the words” section, add is:chats as the filter
- Click on create filter with this result, Select Skip Inbox (Archive), hit ok for both the warnings