From version 4.0 onwards you can find out the client version (for log purposes etc) by logging:
fin.desktop.Excel.version;To confirm you are connecting to the ExcelService you expect you can log/check:
fin.desktop.ExcelService.version;From version 4 you and your end users can confirm you are using the right excel plugin version by looking at Excel.
The message will now say Connected to OpenFin (v x.x.x.x)