User defaults; Starting in CUPS 1.2, user defaults were stored in the ~/.cups directory, and the old ~/.cupsrc and ~/.lpoptions files were deprecated. Support for ~/.cupsrc and ~/.lpoptions have been removed in CUPS 1.5.
IPP test tool; The ipptool IPP test tool is now a first-class user program.
lpadmin; The lpadmin command now supports setting the cupsIPPSupplies and cupsSNMPSupplies keywords in PPDs and deleting options.
CUPS headers; Changes to the main CUPS header may require code changes to applications and toolkits. Users of PPD functions must now include the <cups/ppd.h> header file explicitly since the <cups/cups.h> header no longer does so.
HTTP support: Applications can now set a per-connection timeout interval and callback for HTTP operations as well as query and set SSL/TLS X.509 certificates.
Raster support; The CUPS raster functions now support the creation of PWG Raster files and streams, and a new callback-based context function allows reading and writing from objects other than file descriptors.