One of the changes involves fully transitioning Google Talk to Hangouts. Google Talk was launched in 2005 as a simple chat experience between Gmail users. In 2013, Google replaced Google Talk with Hangouts – and continued to give users the option of using Google Talk. (You might recognize Google Talk as “Gchat” – which appears to be an unofficial name.)
Google feels that Hangouts offer advanced improvements over Google Talk (especially after the introduction of Hangouts Meet and Hangouts Chat). This meant it was now time to say goodbye to Google Talk.
Users within Gmail will get a prompt in the next few weeks inviting them to switch to Hangouts. After June 26, 2017, users will automatically be transitioned to Hangouts. Google suggests that those who really like the way Google Talk looks should use the Dense Roster setting in Hangouts (which Google says provides a similar experience).
Third-party XMPP clients will continue to work with Hangouts for one-on-one chat. However, Google says that XXMP federation with third-party service providers will no longer be supported starting June 26, 2017.
Some people are still using the legacy Google Talk Android app (that was replaced in the Play store in 2013). The legacy app will stop functioning. Google encourages Android users that are affected by this change to install Hangouts now.
Google is retiring the Google+ functionality in Gmail. More specifically, Google is retiring two legacy Google+ features in Gmail: the ability to email Google+ profiles and the use of Google+ Circles. This change is expected to take place “no earlier than April 24, 2017″.