* 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))

  - 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))

- 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))

- `kubectl rollout restart` now works for DaemonSets and StatefulSets. ([#77423](https://github.com/kubernetes/kubernetes/pull/77423), [@apelisse](https://github.com/apelisse))
- `kubectl get --watch=true` now prints custom resource definitions with custom print columns. ([#76161](https://github.com/kubernetes/kubernetes/pull/76161), [@liggitt](https://github.com/liggitt))

- The `batch/v2alpha1` CronJob type definitions and clients are deprecated and removed. ([#96987](https://github.com/kubernetes/kubernetes/pull/96987), [@soltysh](https://github.com/soltysh)) [SIG API Machinery, Apps, CLI and Testing]

- Validation rules for Custom Resource Definitions can be written in the [CEL expression language](https://github.com/google/cel-spec) using the `x-kubernetes-validations` extension in OpenAPIv3 schemas (alpha). This is gated by the alpha "CustomResourceValidationExpressions" feature gate. ([#1...

- Fixed a regression in `1.27.0` that resulted in `missing metadata in converted object` errors when modifying objects for multi-version custom resource definitions with a conversion strategy of `None`. ([#117301](https://github.com/kubernetes/kubernetes/pull/117301), [@ncdc](https://github.com/ncdc))

Kubernetes 1.11, you must keep the following in mind:

* **JSON configuration files that contain fields with incorrect case will no longer be valid. You must correct these files before upgrading.** When specifying keys in JSON resource definitions during direct API server communication, the keys are case-sensitive. A bug introduced in Kubernetes 1.8 caused the API server to accept a request with incorrect case and coerce it to correct case, but this behaviour has been fixed in 1.11 and the...

### Promoted Server Side Unknown Field Validation to Beta