Theoretically any access to Admin pages or Admin functionality should be initiated from the gutensite.com domain, e.g. http://www.gutensite.com/admin

This has always been enforced for regular admin pages. But there were cases where this was not strictly enforced, e.g. the API used to be able to be accessed through yourdomain.com/admin/api/admin, however we are now strictly enforcing it to ensure that the administrative functionality is protected and necessarily secured by an SSL connection that we maintain. So the API URL for the Administrative access should be gutensite.com/api/admin, but the API URL for regular site access (if you are using that) should still be yourdomain.com/api/site since that is based off the specific domain.