Is it possible to install Google Anthos on prem or ist this a pure cloud service? In some cases in might be useful to manage cluster without a cloud connection.
Anthos is an on the cloud service provided by Google. Whilst you might not be able to have a completely isolated installation of Anthos on-prem with zero external access, Anthos on BareMetal allows you to make use of your on prem infrastructure to get the full capabilities of Anthos.
With Anthos on BareMetal the external connectivity is only used for the minimal control plane functionality of managing your clusters via the Cloud Console. Almost all the other components of Anthos reside on-prem in your infrastructure.
Useful resources.
Introduction to Anthos on bare metal by a Developer Advocate at Google.
About Anthos on BareMetal