wsjtx uses a version of the hamlib CAT control library. This library is virtually identical to the the current release version of hamlib. If a wsjtx user wishes to use the hamlib network rig server rigctld to remotely control their transceiver; then this special version of the rigctl client should be used since that too has the modified hamlib code embedded with it.
WSJT-X home page
WSJT-X User’s Guide
Refer to the hamlib documentation.