- Alpha implementation of Kubectl Command Headers: SIG CLI KEP 859 enabled when KUBECTL_COMMAND_HEADERS environment variable set on the client command line.
  - To enable: export KUBECTL_COMMAND_HEADERS=1; kubectl ... ([#98952](https://github.com/kubernetes/kubernetes/pull/98952), [@seans3](https://github.com/seans3)) [SIG API Machinery and CLI]

- Fixed a regression in default 1.27 configurations in kube-apiserver: fixed the AggregatedDiscoveryEndpoint feature (beta in 1.27+) to successfully fetch discovery information from aggregated API servers that do not check `Accept` headers when serving the `/apis` endpoint ([#120360](https://github.com/kubernetes/kubernetes/pull/120360), [@Jefftree](https://github.com/Jefftree)) [SIG API Machinery]

* Fix metrics API group name in audit configuration ([#53493](https://github.com/kubernetes/kubernetes/pull/53493), [@piosz](https://github.com/piosz))
* Use separate client for leader election in scheduler to avoid starving leader election by regular scheduler operations. ([#53793](https://github.com/kubernetes/kubernetes/pull/53793), [@wojtek-t](https://github.com/wojtek-t))

- Fixed a bug that unintentionally overrides custom Accept headers in http (live-/readiness)-probes if the header is in lowercase. ([#114606](https://github.com/kubernetes/kubernetes/pull/114606), [@tuunit](https://github.com/tuunit))

- Leader Migration for controller managers graduated to beta. ([#103533](https://github.com/kubernetes/kubernetes/pull/103533), [@jiahuif](https://github.com/jiahuif)) [SIG API Machinery and Cloud Provider]

- Fixed an issue where kubelet does not set case-insensitive headers for http probes. (#117182, @dddddai) ([#117333](https://github.com/kubernetes/kubernetes/pull/117333), [@dddddai](https://github.com/dddddai)) [SIG API Machinery, Apps and Node]

### Feature

- Added a path `/header?key=` to `agnhost netexec` allowing one to view what the header value is of the incoming request.

  Ex:
  ```
  $ curl -H "X-Forwarded-For: something" 172.17.0.2:8080/header?key=X-Forwarded-For
  something
  ```

- The `--leader-elect*` CLI args are now honored in scheduler. ([#105915](https://github.com/kubernetes/kubernetes/pull/105915), [@Huang-Wei](https://github.com/Huang-Wei))

- 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.

- 'Container `preStop` and `postStart` lifecycle handlers using `httpGet` now
  honor the specified `scheme` and `headers` fields. This enables setting custom
  headers and changing the scheme to `HTTPS`, consistent with container
  startup/readiness/liveness probe capabilities. Lifecycle handlers configured