Chat with classic Hangouts users
If you also use classic Hangouts
Users of the new Hangouts Chat can chat via direct message with users of classic Hangouts.
If a colleague is using classic Hangouts, you can still directly message them with new Hangouts Chat. You'll see direct messages in Hangouts Chat, and your colleague will see the message in classic Hangouts. Note that this only applies to direct messages; group messages cannot be sent across different versions of Hangouts.
If you use both classic Hangouts and new Hangouts Chat, you will only see message notifications in the version from which you send a message. For example, if you send a message in new Hangouts Chat, reply notifications for that message will only be visible in new Hangouts chat. If you send a message in classic Hangouts, replies will only be visible in classic Hangouts.
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.