qBittorrent 4.0 is the first release of the application to drop OS/2 support, as well as support for the old Qt 4 framework as Qt 5.5.1 or later is now required to run it on all supported platforms. It also brings a new logo and a new SVG-based icon theme can be easily scaled.
Lots of other cosmetic changes are present in this release, and the WebGUI received multiple enhancements. Among the new features, we can mention a new UI for managing locally banned IPs, the ability to specify where to save and load config files for portable mode, column toggling in the Trackerlist, a new widget for displaying filesystem paths while typing in the Add New Torrent and Options dialogs, and support for stripping subfolders in multifile torrents.