As mentioned in December 2017, Google starting from April 16, 2019, will transition classic Hangouts users on G Suite domains to Hangouts Chat and Hangouts Meet. Between April and September 2019, Google says that features from classic Hangouts will come to Chat.
In October 2019, support for classic Hangouts for G Suite customers will be ended. On April 16th, 2019, for G Suite domains that have classic Hangouts enabled, Chat will also become available to users on the web and via mobile apps. They can also continue using classic Hangouts in Gmail, mobile, web or the Chrome extension. Admin changes on April 16th will let the chat admin settings control chat capability in both classic Hangouts and Chat.
A new setting in the Admin console under Apps > G Suite > Hangouts Chat will be added so admins can disable classic Hangouts user interfaces at a time of your choosing. The “Google Hangouts” settings page in the Admin console will be renamed “Hangouts Meet.” This setting will control both classic Hangouts video and Hangouts Meet.
Classic Hangouts will be retired for all G Suite customers starting October 2019 and all remaining users will be transitioned to Chat. Between April and September 2019, Google said that it will add more features for users to move from classic Hangouts to Chat. These features include integration with Gmail, chatting with external users, an improved video calling experience, and making calls with Google Voice.