Google Hangouts chat users now see an updated UI with with Status Markers and Contacts in their conversation list in Hangouts in Gmail. To make it easier to view which of your co-workers are online, green bubbles now display on their profile pictures when they’re active on Hangouts—which means fewer conversations start with “Hey, you there?”
Status markers are shown as green bubbles and the displayed contacts are in order of most recent chats. Other features include recent conversation snippets and a new contact search button.
For more information, read Your status and contacts on Hangouts.