- Kubeadm: added the experimental (alpha) feature gate `EtcdLearnerMode` that allows etcd members to be joined as learner and only then promoted as voting members ([#113318](https://github.com/kubernetes/kubernetes/pull/113318), [@pacoxu](https://github.com/pacoxu))

* Websocket requests may now authenticate to the API server by passing a bearer token in a websocket subprotocol of the form `base64url.bearer.authorization.k8s.io.<base64url-encoded-bearer-token>`. ([#47740](https://github.com/kubernetes/kubernetes/pull/47740), [@liggitt](https://github.com/liggitt))

- The helping message of commands which have sub-commands is now clearer and more instructive. It will show the full command instead of `kubectl <command> --help ...`
  

- `kubeadm`: promoted feature gate `EtcdLearnerMode` to `beta`. Learner mode for
  joining `etcd` members is now enabled by default. ([#120228](https://github.com/kubernetes/kubernetes/pull/120228), [@pacoxu](https://github.com/pacoxu))

- Client-go: Optimized leaders renewing leases by updating leader lock optimistically without getting the record from the API server first. Also, a new metric `leader_election_slowpath_total` was added to allow users to monitor how many leader elections are updated non-optimistically.