- Removed deprecated `gogo` protocol definitions from `k8s.io/kubelet/pkg/apis/pluginregistration` in favor of `google.golang.org/protobuf`. ([#132773](https://github.com/kubernetes/kubernetes/pull/132773), [@saschagrunert](https://github.com/saschagrunert))

    - [API Machinery](#api-machinery)
      - [kube-apiserver](#kube-apiserver)
      - [Dynamic Admission Control](#dynamic-admission-control)
      - [Custom Resource Definitions (CRDs)](#custom-resource-definitions-crds)
      - [Garbage Collector](#garbage-collector)
      - [Monitoring/Prometheus](#monitoringprometheus)
      - [Go Client](#go-client)
  - [External Dependencies](#external-dependencies)

  - The built-in `system:csi-external-provisioner` and `system:csi-external-attacher` cluster roles are deprecated and will not be auto-created in a future release. CSI deployments should provide their own RBAC role definitions with required permissions. ([#69868](https://github.com/kubernetes/kubernetes/pull/69868), [@pohly]( https://github.com/pohly))

- Finalizer Protection for Service LoadBalancers is now in beta (enabled by default). This feature...

- Restores compatibility with <=1.15.x custom resources by not publishing OpenAPI for non-structural custom resource definitions ([#82653](https://github.com/kubernetes/kubernetes/pull/82653), [@liggitt](https://github.com/liggitt))

- Ingress:
  - `spec.ingressClassName` replaces the deprecated `kubernetes.io/ingress.class` annotation, and allows associating an Ingress object with a particular controller.

* CustomResourceDefinitions: OpenAPI v3 validation schemas containing `$ref`references are no longer permitted. Before upgrading, ensure CRD definitions do not include those `$ref` fields. ([#58438](https://github.com/kubernetes/kubernetes/pull/58438), [@carlory](https://github.com/carlory))

- OpenAPI definitions served by kube-apiserver now include enum types by default. ([#108898](https://github.com/kubernetes/kubernetes/pull/108898), [@jiahuif](https://github.com/jiahuif))

* CustomResourceDefinitions: OpenAPI v3 validation schemas containing `$ref`references are no longer permitted (valid references could not be constructed previously because property ids were not permitted either). Before upgrading, ensure CRD definitions do not include those `$ref` fields. ([#58438](https://github.com/kubernetes/kubernetes/pull/58438), [@carlory](https://github.com/carlory))

  - The OpenAPI definitions with the prefix "io.k8s.kubernetes.pkg" (deprecated since 1.9) have been removed. ([#74596](https://github.com/kubernetes/kubernetes/pull/74596), [@sttts](https://github.com/sttts))