* [CHANGE] `prometheus_tsdb_storage_blocks_bytes_total` is now `prometheus_tsdb_storage_blocks_bytes`. prometheus/tsdb#506
* [FEATURE] [EXPERIMENTAL] Time overlapping blocks are now allowed; vertical compaction and vertical query merge. It is an optional feature which is controlled by the `--storage.tsdb.allow-overlapping-blocks` flag, disabled by default. prometheus/tsdb#370
* [ENHANCEMENT] Use the WAL for remote_write API. #4588
* [ENHANCEMENT] UI enhancements with upgrade to Bootstrap 4. #5226
* [ENHANCEMENT] Reduce time that Alertmanagers are in flux when reloaded. #5126
* [ENHANCEMENT] Limit number of metrics displayed on UI to 10000. #5139
* [ENHANCEMENT] (1) Remember All/Unhealthy choice on target-overview when reloading page. (2) Resize text-input area on Graph page on mouseclick. #5201
* [ENHANCEMENT] In `histogram_quantile` merge buckets with equivalent le values. #5158.
* [ENHANCEMENT] Show list of offending labels in the error message in many-to-many scenarios. #5189
* [BUGFIX] Fix sorting of rule groups. #5260
* [BUGFIX] Fix support for password_file and bearer_token_file in Kubernetes SD. #5211
* [BUGFIX] Scrape: catch errors when creating HTTP clients #5182. Adds new metrics: