### Apps

- Users can now specify a DataSource/Kind of type `PersistentVolumeClaim` in their PVC spec.  This can then be detected by the external csi-provisioner and plugins if capable. ([#76913](https://github.com/kubernetes/kubernetes/pull/76913), [@j-griffith](https://github.com/j-griffith))

* Protobuf serialization does not distinguish between `[]` and `null`.
API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field)

* Protobuf serialization does not distinguish between `[]` and `null`. ([#45294](https://github.com/kubernetes/kubernetes/pull/45294), [@liggitt](https://github.com/liggitt))

* Protobuf serialization does not distinguish between `[]` and `null`. ([#45294](https://github.com/kubernetes/kubernetes/pull/45294), [@liggitt](https://github.com/liggitt))

* **[stable]** Add support to use NFSv3, NFSv4, and GlusterFS on GCE/GKE GCI image based clusters.
* **[beta]** Added support for mount options in persistent volumes.
* **[alpha]** All in one volume proposal - a new volume driver capable of projecting secrets, configmaps, and downward API items into the same directory.

## Deprecations

Although clusters are enabled to support dual-stack networking, Pods and Services continue to default to single-stack.
To use dual-stack networking: Kubernetes nodes have routable IPv4/IPv6 network interfaces, a dual-stack capable CNI network plugin is used, Pods are configured to be dual-stack and Services have their `.spec.ipFamilyPolicy` field set to either `PreferDualStack` or `RequireDualStack`.

### HorizontalPodAutoscaler v2 graduates to GA