For a complete log of changes to Hamlib, please visit:

http://sourceforge.net/p/hamlib/code/commit_browser

Major changes in 4.0 affecting usage
Most rig model numbers have changed
RIG_LEVEL_VOX has been deprecated and replaced by RIG_LEVEL_VOXDELAY
rigctl 'f' command now returns VFO argument too
rigctl 'y' and 'Y' command now take/show antenna argument and option.
range_list items are undergoing changes towards a different model TBD
RTS/DTR PTT sharing is off by default now -- use serial_share=1 option to
enable