I released devpi-server 6.0.0rc1 at https://m.devpi.net/fschulze/devpi60/devpi-server/6.0.0rc1 for testing.
You should use a testing/staging environment or have working backups before trying this release.
This release doesn't require an export/import cycle and it should be possible to downgrade again as long as you don't use new options on any index. If you use replicas, you now need to share a common secret file with the master and you should read the changelog for a caveat when downgrading.
There are several previously deprecated things removed in this release, some changes in behaviour and several new features. Read the changelog for the details.
Regards, Florian Schulze