- Added a new alpha API: ClusterTrustBundle (`certificates.k8s.io/v1alpha1`).
  A ClusterTrustBundle may be used to distribute [X.509](https://www.itu.int/rec/T-REC-X.509) trust anchors to workloads within the cluster. ([#113218](https://github.com/kubernetes/kubernetes/pull/113218), [@ahmedtd](https://github.com/ahmedtd)) [SIG API Machinery, Auth and Testing]

- Updated incorrect description of persistentVolumeClaimRetentionPolicy ([#126545](https://github.com/kubernetes/kubernetes/pull/126545), [@yangjunmyfm192085](https://github.com/yangjunmyfm192085)) [SIG API Machinery, Apps and CLI]

- kubelet: added `KubeletConfiguration.subidsPerPod`. ([#130028](https://github.com/kubernetes/kubernetes/pull/130028), [@AkihiroSuda](https://github.com/AkihiroSuda)) [SIG API Machinery and Node]

 - Kubernetes is built using golang 1.17. This version of go removes the ability to use a `GODEBUG=x509ignoreCN=0` environment setting to re-enable deprecated legacy behavior of treating the CommonName of X.509 serving certificates as a host name. This behavior has been disabled by default since Kubernetes 1.19 / go 1.15. Serving certificates used by admission webhooks, custom resource conversion webhooks, and aggregated API servers must now include valid...

- Kubernetes is now built with golang 1.15.0-rc.1.