CDN Interconnect isn't the same as Cloud CDN (sorry, the names aren't great).

Cloud CDN itself (https://cloud.google.com/cdn) has been GA for a while, but support for reaching GCS directly from our Load Balancer (https://cloud.google.com/compute/docs/load-balancing/http/us...) and therefore CDN support is in Beta.

Disclosure: I work on Google Cloud.