Back in 2013, Google launched the Google Apps Admin SDK, and later announced as a result that several outdated Apps Admin APIs would be deprecated and shut down in April 2015. Today, they are continuing this effort of removing older, less-used functionality by announcing the deprecation of the GData Admin Settings API. Some GData API functionality will find a replacement from an Admin SDK counterpart, while other features will be discontinued.
To summarize, the GData Admin Settings API is being deprecated today and will remain operational for one year to give developers time to migrate. This means that on August 16, 2017, this deprecated API will be shut down. At that time, all calls to the API and any features in your applications that depend on it will no longer work. Please migrate as soon as possible.