upgrading a cluster, all objects in resource.k8s.io/v1alpha1 (ResourceClaim, ResourceClaimTemplate,
  ResourceClass, PodScheduling) must be deleted. The changes are internal, so
  YAML files which create pods and resource claims don't need changes except for
  the newer `apiVersion`. ([#116299](https://github.com/kubernetes/kubernetes/pull/116299), [@pohly](https://github.com/pohly))

	1. In Namespaces that previously had the "DefaultDeny" annotation,
	   you can create equivalent v1 semantics by creating a
	   NetworkPolicy that matches all pods but does not allow any
	   traffic:

	   ```yaml
           kind: NetworkPolicy
           apiVersion: networking.k8s.io/v1
           metadata:
             name: default-deny
           spec:
             podSelector:
	   ```

   ([#122530](https://github.com/kubernetes/kubernetes/pull/122530), [@neolit123](https://github.com/neolit123))

- Protobuf serialization of metav1.MicroTime timestamps (used in `Lease` and `Event` API objects) has been corrected to truncate to microsecond precision, to match the documented behavior and JSON/YAML serialization. Any existing persisted data is truncated to microsecond when read from etcd. ([#111936](https://github.com/kubernetes/kubernetes/pull/111936), [@haoruan](https://github.com/haoruan))

- Updated the generic apiserver library to produce an error if a new API server is configured with support for a data format other than JSON, YAML, or Protobuf. ([#121325](https://github.com/kubernetes/kubernetes/pull/121325), [@benluddy](https://github.com/benluddy)) [SIG API Machinery]