* Kubernetes now supports transparent compression of API responses. Clients that send `Accept-Encoding: gzip` will now receive a GZIP compressed response body if the API call was larger than 128KB.  Go clients automatically request gzip-encoding by default and should see reduced transfer times for very large API requests.  Clients in other languages may need to make changes to benefit from compression. ([#77449](http...

- `RequestedToCapacityRatioArgs` encoding is now strict ([#91603](https://github.com/kubernetes/kubernetes/pull/91603), [@pancernik](https://github.com/pancernik)) [SIG Scheduling]

    - Uses debian-base:buster-v1.2.0 ([#94733](https://github.com/kubernetes/kubernetes/pull/94733), [@justaugustus](https://github.com/justaugustus)) [SIG API Machinery, Release and Testing]

### Documentation

- Graduating `pod_scheduling_duration_seconds`, `pod_scheduling_attempts`, `framework_extension_point_duration_seconds`, `plugin_execution_duration_seconds` and `queue_incoming_pods_total` metrics to stable. ([#106266](https://github.com/kubernetes/kubernetes/pull/106266), [@ahg-g](https://github.com/ahg-g)) [SIG Instrumentation, Scheduling and Testing]

* Replica set conditions API ([#33905](https://github.com/kubernetes/kubernetes/pull/33905), [@kargakis](https://github.com/kargakis))
* etcd3: avoid unnecessary decoding in etcd3 client  ([#34435](https://github.com/kubernetes/kubernetes/pull/34435), [@wojtek-t](https://github.com/wojtek-t))

### Other (Cleanup or Flake)

- Kube-apiserver: sets an upper-bound on the lifetime of idle keep-alive connections and time to read the headers of incoming requests ([#103958](https://github.com/kubernetes/kubernetes/pull/103958), [@liggitt](https://github.com/liggitt)) [SIG API Machinery and Node]

## Dependencies

### Added
_Nothing has changed._

- 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
  ```

* kube-apiserver: fixed a bug that could cause a goroutine leak if the apiserver encountered an encoding error serving a watch to a websocket watcher ([#84693](https://github.com/kubernetes/kubernetes/pull/84693), [@tedyu](https://github.com/tedyu))

be migrated at the current time using the official Kubernetes procedure.

1.6 will also default to protobuf encoding if using etcd3.  **This change is
irreversible.**  To rollback, you must restore from a backup made before the
protobuf/etcd3 switch, and any changes since the backup will be lost.  As 1.5
does not support protobuf encoding, if you roll back to 1.5 after upgrading to

- JWTs used in service account and OIDC authentication are now strictly parsed to confirm that they use compact serialization. Other encodings were not previously accepted, but would result in different unspecific errors. ([#123540](https://github.com/kubernetes/kubernetes/pull/123540), [@enj](https://github.com/enj))