- Added alpha metrics for compatibility versioning ([#131842](https://github.com/kubernetes/kubernetes/pull/131842), [@michaelasp](https://github.com/michaelasp)) [SIG API Machinery, Architecture, Instrumentation and Scheduling]

  The `flowcontrol.apiserver.k8s.io/v1beta3` APIs are deprecated and will no longer be served in v1.32. All existing objects are available...

### Windows containerd support graduates to beta

Initially introduced in Kubernetes 1.18, Windows containerd support goes to Beta on this release. This includes the added support for Windows Server version 2004 (complete version compatibility can be found in the [documentation for Windows](https://kubernetes.io/docs/setup/production-environment/windows/intro-windows-in-kubernetes/#cri-containerd)).

SIG Windows is also including several addition to this release:

* Switched intstr.Type to sized integer to follow API guidelines and improve compatibility with proto libraries ([#83956](https://github.com/kubernetes/kubernetes/pull/83956), [@liggitt](https://github.com/liggitt))

{Object} client rect\n */\nexport default function getBoundingClientRect(element) {\n  let rect = {};\n\n  // IE10 10 FIX: Please, don't ask, the element isn't\n  // considered in DOM in some circumstances...\n  // This isn't reproducible in IE10 compatibility mode of IE11\n  try {\n    if (isIE(10)) {\n      rect = element.getBoundingClientRect();\n      const scrollTop = getScroll(element, 'top');\n      const scrollLeft = getScroll(element, 'left');\n      rect.top += scrollTop;\n      rect.left +=...

* Fixes `kubectl create secret docker-registry` compatibility ([#72344](https://github.com/kubernetes/kubernetes/pull/72344), [@liggitt](https://github.com/liggitt))

- Changes to timeout parameter handling in 1.20.0-beta.2 have been reverted to avoid breaking backwards compatibility with existing clients. ([#96727](https://github.com/kubernetes/kubernetes/pull/96727), [@liggitt](https://github.com/liggitt)) [SIG API Machinery and Testing]

## Changes by Kind

### API Change

- Aggregated discovery now returns `responseKind: {}` for resources which are missing group/version/kind information, to ensure compatibility with v0.26.0-v0.26.3 clients. ([#119835](https://github.com/kubernetes/kubernetes/pull/119835), [@liggitt](https://github.com/liggitt)) [SIG API Machinery and Testing]

### Feature

* Fixes `kubectl create secret docker-registry` compatibility ([#72344](https://github.com/kubernetes/kubernetes/pull/72344), [@liggitt](https://github.com/liggitt))

## Changelog since v1.15.3

### Other notable changes

* Restores compatibility with kubectl client-side validation when structural schemas are present in a CRD which sets spec.preserveUnknownFields=true ([#82666](https://github.com/kubernetes/kubernetes/pull/82666), [@liggitt](https://github.com/liggitt))