For physical zone separation you need to check the `supportsPzs` attribute when listing the zones (e.g. https://cloud.google.com/compute/docs/reference/rest/v1/zone..., but you should be able to find many other places where this attribute is surfaced).
Random datacenters should start advertising availability zones since they should have different fault domains anyway. Google can get away with this, why can't smaller companies?
It says "reserved for future use" but other docs mentioned "physical zone separation": https://googleapis.dev/java/google-api-services-compute/alph...