Download Firmware Version 184.108.40.206 for the EF 400mm f/2.8L IS III USM and EF 600mm f/4L IS III USM.
Cameras that can be used to run the lens’ firmware update are listed below: (As of March 2019)
EOS-1D X Mark II, EOS-1D X, EOS-1D C, EOS 5Ds, EOS 5DsR, EOS 5D Mark IV, EOS 5D Mark III,
EOS 6D Mark II, EOS 6D, EOS 7D Mark II, EOS 80D, EOS 70D,
EOS Rebel T7i, EOS REBEL SL2, EOS REBEL T6i, EOS REBEL T5i, EOS REBEL SL1, EOS REBEL T4i,
M50, EOS M6, EOS M5, EOS M3, EOS M2, EOS M, EOS M100, EOS M10,
EOS R, EOS RP
Note: If using a EOS R or EOS M series camera to update the lens’ firmware, a mount adaptor is required.
Note: If you are not able to perform the firmware update, please contact Canon Customer Service Center and follow the Workaround procedures listed below.