Google Site Search is being discontinued according to multiple reports. Google emailed its Site Search customers saying that starting April 1, 2017, new purchased and renewals of GSS will not be available. The product will completely shut down on April 1, 2018.
They noted that this move will not have any impact on a customers current use of Google Site Search or until your license expires. Customers will continue to receive customer and technical support for the duration of their license.
The rest of the email from Google's Enterprise Search Team provides some additional insights:
"Search has always been core to Google and we know its essential to the way your customers find content and interact with your website," wrote the Google's Enterprise Search Team. "While Google Cloud will no longer support GSS, we're continuing to invest in other technologies that make enterprise search a great experience for our customers. Recently, we introduced the general availability of Google Cloud Search, which searches across G Suite content, providing useful and actionable information and recommendations."
"When your GSS subscription expires or your quota is exhausted, your subscription will automatically convert to Custom Search Engine (CSE)," noted Google. "Custom Search Engine is an ad-supported product that provides similar capabilities to GSS, including the ability to build custom search engines for sites or pages, image search for your website, and customize the look and feel of search results."
The Google Enterprise Search Team noted that there are difference between differences between GSS and CSE.