- The `DeclarativeValidation` feature gate is enabled by default. When enabled, mismatches with existing hand written validation is reported via metrics.

 - Scheduler's CycleState now embeds internal read/write locking inside its `Read()` and `Write()` functions. Meanwhile, `Lock()` and `Unlock()` function are removed. Scheduler plugin developers are now required to remove `CycleState#Lock()` and `CycleState#Unlock()`. Just simply use `Read()` and `Write()` as they're natively thread-safe now. ([#101542](https://github.com/kubernetes/kubernetes/pull/101542), [@Huang-Wei](http...

- The PodDisruptionBudget API has been promoted to policy/v1 with no schema changes. The only functional change is that an empty selector (`{}`) written to a policy/v1 PodDisruptionBudget now selects all pods in the namespace. The behavior of the policy/v1beta1 API remains unchanged. The policy/v1beta1 PodDisruptionBudget API is deprecated and will no longer be served in 1.25+. ([#99290](https://...

  * Log warning when invalid dir passed to `kubectl proxy --www` ([#44952](https://github.com/kubernetes/kubernetes/pull/44952), [@CaoShuFeng](https://github.com/CaoShuFeng))

  * Add `--write-config-to` flag to kube-proxy to allow users to write the default configuration settings to a file. ([#45908](https://github.com/kubernetes/kubernetes/pull/45908), [@ncdc](https://github.com/ncdc))

* Fix serialization of EnforceNodeAllocatable ([#44606](https://github.com/kubernetes/kubernetes/pull/44606), [@ivan4th](https://github.com/ivan4th))
* Add --write-config-to flag to kube-proxy to allow users to write the default configuration settings to a file. ([#45908](https://github.com/kubernetes/kubernetes/pull/45908), [@ncdc](https://github.com/ncdc))

* RBAC objects are now stored in etcd in v1 format. After completing an upgrade to 1.9, RBAC objects (Roles, RoleBindings, ClusterRoles, ClusterRoleBindings) should be migrated to ensure all persisted objects are written in `v1` format, prior to `v1alpha1` support being removed in a future release. ([#52950](https://github.com/kubernetes/kubernetes/pull/52950), [@liggitt](https://github.com/liggitt))

### Other notable changes

 - Log messages in JSON format are written to stderr by default now (same as text format) instead of stdout. Users who expected JSON output on stdout must now capture stderr instead or in addition to stdout. ([#106146](https://github.com/kubernetes/kubernetes/pull/106146), [@pohly](https:...

* **Multiple schedulers**
  * Modify your PodSpecs that currently use the `scheduler.alpha.kubernetes.io/name` annotation on Pod, to instead use the `schedulerName` field in the PodSpec.
  * Modify any custom scheduler(s) you have written so that they read the `schedulerName` field on Pod instead of the `scheduler.alpha.kubernetes.io/name` annotation.
  * Note that you can only start using the `schedulerName` field **after** you upgrade to 1.6; it is not recognized in 1.5.

- Kubectl cluster-info dump changed to only display a message telling you the location where the output was written when the output is not standard output. ([#88765](https://github.com/kubernetes/kubernetes/pull/88765), [@brianpursley](https://github.com/brianpursley)) [SIG CLI]

* Check if container memory stats are available before accessing it ([#77656](https://github.com/kubernetes/kubernetes/pull/77656), [@yastij](https://github.com/yastij))
* client-go and kubectl no longer write cached discovery files with world-accessible file permissions ([#77874](https://github.com/kubernetes/kubernetes/pull/77874), [@yuchengwu](https://github.com/yuchengwu))