code: def _read_capabilities(self):
          
  
          frame = yubikey_frame.YubiKeyFrame(command=SLOT.YK4_CAPABILITIES)
          self._device._write(frame)
          response = self._device._read_response()
          r_len = yubico_util.ord_byte(response[0])
  
          # 1 byte length, 2 byte CRC.
          if not yubico_util.validate_crc16(response[:r_len+3]):
              raise YubiKey4_USBHIDError("Read from device failed CRC check")
  
          return response[1:r_len+1]
docs: Read the capabilities list from a YubiKey >= 4.0.0