As of this writing, I have received a legitimate and valid email from Google that Google Hangouts will be upgraded to Google Chat. Since the instructions from Google is long, here’s my take on how I back up my Google Hangouts conversations.

1. Go to https://takeout.google.com/
2. Deselect all items that are selected in default.
3. Scroll down and check the Google Hangouts item.
4. Click the Next Step button.
5. Choose if .zip or .tgz format.
6. A large file is split in default if exceeding 2GB.
7. Waiting time depends on how large the date will be i.e. too many conversations, large exported file size.
8. Download exported file.