Sorry, no shiny new features on this one. But a lot of std::string const & parameters are now either std::string_view or (if we're passing them on to the C-level library) pqxx::zview. Depending on how exactly you call those functions, it may speed up your code by eliminating some implicit string constructions and heap buffer allocations. Also some little compile fixes, of course.
Under the hood, though, it's a different story. I broke up the biggest inheritance hierarchy, which included almost all the major classes: the transaction classes, pipeline, streams, and so on. It is now two, much smaller, inheritance hierarchies. It rids us of the one case of virtual inheritance that the library had.
You may hit some minor compile problems with the changed parameter types. If you built your own transaction classes, you'll have to deal with some major changes. In the longer run we're going to drop the ability to plug your own transaction types into the hierarchy, and make more things final.