This release finishes the mutation of Nominatim into a Python package. The PHP frontend, bundled osm2pgsql and cmake build scripts have been removed, making Nominatim easier to install and maintain.
Also in this release, the osm2pgsql import style configuration has been largely be rewritten. If you are using one of the built-in styles, this will not make much of a difference. If you are maintaining your own custom style, however, this should become much easier. Have a look at the documentation of the pull request for an overview of the changes. The changes are backwards-compatible, so your old scripts will keep working for now.
Finally, Nominatim has a new hook for adding pre-processing functions for incoming search queries, allowing to apply custom filtering. The first filter to use this new functionality breaks up Japanese addresses into their parts. Many thanks to @miku0 for this code.
A more complete list of changes can be found in the Changelog.
If you are already using the Python frontend and pip installation method, then updating is straightforward. If not, it is strongly recommended that you update to version 4.5 first, switch frontend and installation code and then update to the new version 5.0. As always, read through the migration guide before updating.