Hi Owen,
There is new version of GstarCAD 2023 (https://www.gstarcad.net/cad/) and I have recived link to SDK for 2023:
http://www.gstarcad.pl/ftp/2023/GRX/grxsdk_GstarCAD_2023.zip
I beleve it help with supporting GS in new OpenDCL.
Regards
Mateusz Jacak