I'm afraid you're probably right, but there is nothing out there yet about the original API's deprecation. It was announced a few years ago that it would be replaced, and any new applications should use the newer API, but there has never been an official announcement of its demise.
This happened a couple of years ago and when I brought up the issue it was discovered that a DNS cname record had been removed for this endpoint. That was restored and the issue was fixed. I was hoping that this is the same thing. I have planned a v2 version of my PowerShell module that uses the new API for the past year, but haven't been able to revisit this project.