Current slice frequency question

I have to ask since I been trying to find this for a while. When starting my custom program I want to determine the current rig frequency of the slice/vfo. It appears I can only do this with the API if I subscribe to the slice then change the frequency with the knob which then reports each frequency change via the udp. However if I use CAT then all I have to do is issue the zzfa, fa, zzfb, or fb commands to instantly get the frequency without any other info. So the question, is there an api command or something in the api that allows me to get the current slice/vfo frequency without changing it upon startup?