Canon has announced a firmware update for the new 1D Mark IV. The update has not yet been released, and is due in late January. The new firmware 1.0.6 enhances AF tracking performance. There is also a firmware update 2.0.0 on the Canon USA website that is specific to the wireless file transmitter.
From the Canon USA website.
â€œThis firmware update (Version 2.0.0) is for the WFT-E2/E2A to make these
wireless file transmitters compatible with the EOS-1D Mark IV. This firmware
update is not necessary if the wireless file transmitters are not used.â€