Google first announced its intention to discontinue support for JSON-RPC protocol and Global HTTP Batch in its APIs in 2018. Its original timetable was to discontinue support in March of 2019. That timetable was extended, but the new deadline is fast approaching. The new deprecation date is August 12, 2020.
Starting in February, and running through August of this year, Google has scheduled downtime for both JSON-RPC and Global HTTP Batch to allow users to identify their systems that rely on these features. Google updates the scheduled downtime schedule from time to time. The most up to date schedule will always be posted to this blog post.
For developers looking to test if they rely on JSON-RPC, two options are available. First, send a request to https://www.googleapis.com/rpc. Alternatively, send a request to https://content.googleapis.com/rpc.
Regarding HTTP batch, developers forming homogenous batch requests using Google API Client Libraries, non-Google API client libraries, or no library should migrate. For more details on how to migrate away from these outdated features, follow instructions at Google's blog post announcement.