We released Code Owners 4.0 on 🎉
Download on the Atlassian Marketplace for Data Center and Server
New Features
New Merge Checks:
based on active Code Owners groups
defined in CODEOWNERS file, beside the regular owner rules
possibility to combine several checks with either OR relation
The two existing options to define merge checks was for many of our customers too restrictive and did not match their workflows.
Therefor we added a more flexible option to define merge checks.
Check out our new Merge Checks guide to learn how to use them.
Option to disable Code Owners for some repositories
Merge Checks was already an Opt-In feature per repo base.
We added an option to Opt-Out from auto-assignment of Code Owners as reviewers to newly created or updated pull requests.
If you want to disable Code Owners e.g in a forked repository, you just need to turn the
auto-assignment off in the repository settings of the fork.
Or if you have a big group of potential reviewers and you want to enforce that some must review, but your team should decide for each pull request, who that should be? Enable and configure your Merge Checks and disable the auto-assignment. The Code Owners tooltip in pull request creation wizard will still help you to choose the right person as reviewers.
Improvements
Debug Logging switch in global app settings
Admins can turn on Debug logging for Code Owners by simple toggle a switch in the global settings of the Code Owners app. And again off of course, after you have sent us the logs for support cases. 
Removed support for Bitbucket Server 5.x
Since Bitbucket Server 5.x reached end of life, we removed support for it in Code Owners 4.0 .
Changelog
4.0.0: resolved issues on
Features and Improvements mentioned above.
Previous: Release Notes v3.1
Do you have any questions, suggestions, or problems?
Let us know. We’re glad to help!