* The kube-apiserver `--storage-version` flag has been removed; you must use `--storage-versions` instead. ([#61453](https://github.com/kubernetes/kubernetes/pull/61453), [@hzxuzhonghu](https://github.com/hzxuzhonghu))
* Authors of aggregated API servers must not rely on authorization being done by the kube-apiserver, and must do delegated authorization in addition. ([#61349](https://github.com/kubernetes/kubernetes/pull/61349), [@sttts](https://github.com/sttts))

- Flex volume plugins now support expandvolume (to increase underlying volume capacity) and expanfs (resize filesystem) commands that Flex plugin authors can implement to support expanding in use Flex PersistentVolumes ([#67851](https://github.com/kubernetes/kubernetes/pull/67851), [@aniket-s-kulkarni](https://github.com/aniket-s-kulkarni))

This release also contains a number of bug fixes to the feature set. Aspiring plugin authors can look at [sample-exec-plugin](https://github.com/ankeesler/sample-exec-plugin) as a way to get started.

- The alpha Dynamic Resource Allocation gRPC API is still available, but might be removed in future releases. Driver authors should update their DRA drivers to use the v1beta1 gRPC API. ([#128646](https://github.com/kubernetes/kubernetes/pull/128646), [@pohly](https://github.com/pohly)) [SIG Node and Testing]

[RollingUpdate](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#rolling-updates) and [OnDelete](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#on-delete) update strategies.

* [alpha] StatefulSet authors should be able to relax the [ordering](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#orderedready-pod-management) and [parallelism](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#parallel-pod-management)...