This release brings improvements to how address ranks are computed and place nodes and boundaries are linked. You can now expect better results in the classification of address details. It is now also possible to have country-specific address ranking to account for local deviations.
Thanks to last years Google Summer of Code, the Wikipedia ranking has been improved. It is now based on a recent Wikipedia dump with a lot more pages and Nominatim can also take into account Wikidata tags when linking.
The code has seen more restructuring. The C indexer has been replaces by a simplified Python script and we have started to split up the larger SQL functions into more readable chunks.
A full list of changes can be found as usual in the Changelog.md.
If you want to update from 3.x.x, there is a database migration path described in the migration guide. Migrating from 3.1.0 can be done without problems. When updating from 3.0.x, a full database reimport is strongly recommended. Updating from older releases is only possible with a database reimport.