Chat with classic Hangouts users
If you also use classic Hangouts
Users of 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 Hangouts Chat. You'll see direct messages in Hangouts Chat, and your colleague will see the message in classic Hangouts. This compatibility only applies to direct messages; group messages can't be sent across different versions of Hangouts.
If you use both classic Hangouts and Hangouts Chat, you'll only see message notifications in the version you send a message from. For example, if you send a message in Hangouts Chat, reply notifications for that message will only be visible in 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 won't be edited or deleted for users in classic Hangouts.
If you chat with a classic Hangouts user who changes their chat history setting, a new conversation thread will start in Hangouts Chat that reflects this setting change.