The main themes of this release are:

- **Custom resources:** CRDs are in widespread use as a way to extend Kubernetes to persist and serve new resource types, and have been available in beta since the 1.7 release. The 1.16 release marks the graduation of CRDs to general availability (GA).

- Fixed a bug that prevents kubectl to validate CRDs with schema using x-kubernetes-preserve-unknown-fields on object fields.

- Reduce API server memory when many CRDs are loaded by sharing a single etcd3 client logger across all clients ([#111648](https://github.com/kubernetes/kubernetes/pull/111648), [@negz](https://github.com/negz)) [SIG API Machinery]

- Reduce API server memory when many CRDs are loaded by sharing a single etcd3 client logger across all clients ([#111650](https://github.com/kubernetes/kubernetes/pull/111650), [@negz](https://github.com/negz)) [SIG API Machinery]

- Reduce API server memory when many CRDs are loaded by sharing a single etcd3 client logger across all clients ([#111649](https://github.com/kubernetes/kubernetes/pull/111649), [@negz](https://github.com/negz)) [SIG API Machinery]

#### Extensibility

- The community has been asking for continuing support of extensibility, so this cycle features more work around CRDs and API Machinery. Most of the enhancements in this cycle were from SIG API Machinery and related areas.

### Extensibility around core Kubernetes APIs

#### CustomResourceDefinitions Pruning

* Transition CSINodeInfo and CSIDriver alpha CRDs to in-tree CSINode and CSIDriver core storage v1beta1 APIs. ([#74283](https://github.com/kubernetes/kubernetes/pull/74283), [@xing-yang](https://github.com/xing-yang))
    * ACTION REQUIRED: the alpha CRDs are no longer used and drivers will need to be updated to use the beta APIs.

- `ValidatingAdmissionPolicy` type checking now supports CRDs and API extensions types. ([#119109](https://github.com/kubernetes/kubernetes/pull/119109), [@jiahuif](https://github.com/jiahuif))