([#64792](https://github.com/kubernetes/kubernetes/pull/64792), [@luxas](https://github.com/luxas))

- Number of errors reported to the metric `storage_operation_duration_seconds_count` for emptyDir decreased significantly because previously one error was reported for each projected volume created. ([#117022](https://github.com/kubernetes/kubernetes/pull/117022), [@mpatlasov](https://github.com/mpatlasov)) [SIG Storage]

- Improved exponential backoff in Reflector, significantly reducing the load on Kubernetes apiserver in case of throttling of requests. ([#118132](https://github.com/kubernetes/kubernetes/pull/118132), [@marseel](https://github.com/marseel)) [SIG API Machinery and Scalability]

### Bug or Regression

- An inefficient lock in EndpointSlice controller metrics cache has been reworked. Network programming latency may be significantly reduced in certain scenarios, especially in clusters with a large number of Services. ([#107169](https://github.com/kubernetes/kubernetes/pull/107169), [@robscott](https://github.com/robscott)) [SIG Apps and Network]

    Potential impacts:
    If an SLO/alert has been defined based on `volume_operation_total_seconds`, it might get violated because of the more accurate metric might be significantly larger than previously reported. The metric is defined to be a histogram and the new semantic could change the distribution. ([#78061](https://github.com/kubernetes/kubernetes/pull/78061), [@yuxiangqian](https://github.com/yuxiangqian))

- Number of errors reported to the metric `storage_operation_duration_seconds_count` for emptyDir decreased significantly because previously one error was reported for each projected volume created. ([#117022](https://github.com/kubernetes/kubernetes/pull/117022), [@mpatlasov](https://github.com/mpatlasov)) [SIG Storage]

## Before Upgrading

Consider the following changes, limitations, and guidelines before you upgrade:

### **API Machinery**

* Use KubeDNS by default in GCE setups, as CoreDNS has significantly higher memory usage in large clusters. ([#68629](https://github.com/kubernetes/kubernetes/pull/68629), [@shyamjvs](https://github.com/shyamjvs))

### Other notable announcements

SIG Network is moving IPv6 to Beta in Kubernetes 1.18, after incrementing significantly the test coverage with new CI jobs.

* Ensure the GCI metadata files do not have newline at the end ([#38727](https://github.com/kubernetes/kubernetes/pull/38727), [@Amey-D](https://github.com/Amey-D))
* Significantly speed-up make ([#38700](https://github.com/kubernetes/kubernetes/pull/38700), [@sttts](https://github.com/sttts))