- Simplied validation error message for invalid fields by removing redundant field name. ([#132513](https://github.com/kubernetes/kubernetes/pull/132513), [@xiaoweim](https://github.com/xiaoweim)) [SIG API Machinery, Apps, Auth, Node and Scheduling]

  `hostAliases` fields to mark the fields used as keys in those lists as either defaulted
  or required. ([#124553](https://github.com/kubernetes/kubernetes/pull/124553), [@pmalek](https://github.com/pmalek))

  If the `DeclarativeValidation` feature gate is enabled, mismatches with existing validation are reported via metrics.

 * kubeadm: The Token-related fields in the `MasterConfiguration` object have now been refactored. Instead of the top-level `.Token`, `.TokenTTL`, `.TokenUsages`, `.TokenGroups` fields, there is now a `BootstrapTokens` slice of `BootstrapToken` objects that support the same features under the `.Token`, `.TTL`, `.Usages`, `.Groups` fields. ([#64408](https://github.com/kubernetes/kubernetes/pull/64408), [@luxas](https://github.com/luxas))...

### API Change

- Add Probe-level terminationGracePeriodSeconds field ([#99375](https://github.com/kubernetes/kubernetes/pull/99375), [@ehashman](https://github.com/ehashman)) [SIG API Machinery, Apps, Node and Testing]

### Other notable changes

API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field)
can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6).

    * API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field) can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6+). JSON API clients should tolerate `null` values for such fields, and treat `null` and `[]` as equivalent in meaning unless specifically documented...

    * API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field) can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6+). JSON API clients should tolerate `null` values for such fields, and treat `null` and `[]` as equivalent in meaning unless specifically documented...