Chat with classic Hangouts users
If you also use classic Hangouts
You can exchange direct messages with others in your domain who are using classic Hangouts. You'll see direct messages in Hangouts Chat, while the other user will see them in classic Hangouts. Note that this only applies to one-on-one direct messages; group messages do not appear across different versions of Hangouts.
Because Hangouts Chat messages are sent to classic Hangouts, you can also use classic Hangouts if you're running both products. To avoid sending you double notifications, only Hangouts Chat will send you a notification for any replies. Similarly, if you begin chatting with someone in classic Hangouts, you won't receive notifications for that chat from Hangouts Chat.
Editing and deleting messages
If you edit or delete a message in Hangouts Chat, the message will not be edited or deleted for users on classic Hangouts.
If you chat with a classic Hangouts user who changes the chat history setting, a new conversation thread will start in Hangouts Chat that reflects this setting change.