Google is shutting the Hangouts API, so that even existing apps that use it will cease working from April onwards.
The closure wasn't announced or blogged about; instead, it appeared as an update to the Google Hangouts API FAQ, and in an email sent to developers actively using the API.
The news wasn't totally unexpected; Google talked a lot about Allo and Duo at Google I/O in September, two apps that replicate many of the features of Hangouts, and while waxing lyrical about the new options, no mention at all was made of Hangouts. Then came the news that Google's Pixel phone comes with Hangouts disabled by default in favor of Allo and Duo.
In fact, when Allo and Duo were launched back in August, Google's VP for communications Nick Fox said that Hangouts would be increasingly focused on enterprise applications, leaving Duo and Allo for the mobile phone sector. At the time, Fox said that Hangouts is used heavily in enterprises and group collaborations, and that it would be developed as a competitor to Microsoft Office, becoming increasingly more integrated with the Google Apps suite.
The announcement on the FAQ seems to back up this earlier assessment. According to the FAQ, most new apps will no longer be accepted, while existing apps will no longer function after April 25th. There are some exceptions, including the ability to dial into a call (served by the Dialpad and RingCentral apps), integrations with other enterprise communications tools (e.g. Slack), and Google's own Hangouts on Air broadcasting tools (Toolbox, Control Room, Cameraman).
An email sent to active users of the Hangouts API also emphasizes the change of direction, saying that the API:
"was originally intended to support social scenarios for consumer users as part of Google+, whereas Hangouts is now turning to focus on enterprise use cases.”
The fact that Hangouts has a future in Google won't, of course, be much comfort to developers who have put time and effort into developing apps using the API. They may justifiably feel that Google's track record in summarily closing services makes it a difficult company to trust.