Rhino 6 has following Cycles commands:
RhinoCycles_ChangeSamples
RhinoCycles_ClearTextureMemory
RhinoCycles_ListDevices
RhinoCycles_SelectDevice
RhinoCycles_SetAdvancedOptions
RhinoCycles_SetDebugOptions
RhinoCycles_SetRenderOptions
RhinoCycles_SetThreads
RhinoCycles_ShowDeviceCapabilities
All these commands are undocumented.