I believe there's no requirement if you just want to use Anthos on GKE (I could be wrong though, Anthos is relatively new).
Alternatively, if what you really want is the ease to manage and deploy containers and automatically scale according to traffic, my understanding is you can always use the open source Knative project with your Kubenetes cluster. This provide you the exact same API supported by Cloud Run and makes it very easy to migrate from managed Cloud Run to on-prem K8s cluster (or K8s clusters from other Cloud vendors).
thanks, I hope you're right, GCP doesn't appear to be clear on this point, seems to be offering free trial up to May 2020 and then who know. I'm aware of the ability to set it up from open source which is a great fallback!
Alternatively, if what you really want is the ease to manage and deploy containers and automatically scale according to traffic, my understanding is you can always use the open source Knative project with your Kubenetes cluster. This provide you the exact same API supported by Cloud Run and makes it very easy to migrate from managed Cloud Run to on-prem K8s cluster (or K8s clusters from other Cloud vendors).