DeepCopy Error When Importing client-go

I would like to create Istio Gateways from a controller. When I import “istio.io/client-go/pkg/apis/networking/v1alpha3” to be able to create client-go compatible objects, I get errors like: vendor/istio.io/client-go/pkg/apis/networking/v1alpha3/zz_generated.deepcopy.gen.go:16:9: in.Spec.DeepCopyInto undefined (type v1alpha3.DestinationRule has no field or method DeepCopyInto)

What am I doing wrong?