From Canon USA's site:
Thank you for using Canon products.
EOS 5D Mark III Digital SLR Camera
EOS-1D X Digital SLR Camera
Depending upon the shooting conditions, it may take slightly longer for the EOS 5D Mark III and EOS-1D X digital SLR cameras to acquire focus when using the Speedlite's AF Assist Beam, compared with that of the EOS 5D Mark II and EOS-1D Mark IV digital SLR cameras using the Speedlite's AF Assist Beam.
We are developing a solution to enhance the focusing feature for the EOS 5D Mark III and EOS-1D X and plan to release a firmware update based on following estimated schedule:
EOS 5D Mark III: (estimated) Late April, 2013
EOS-1D X: (estimated) Late May, 2013
First, it was f/8 AF then the clean HDMI out. Canon has also said they will update the AF-Assist issue, but it came later, and will likely be rolled up in a furure update.
So this update does not address the issue with AF-assist beam lag. Is that a separate update?
I was wondering this myself as the Canon website does not specifically mention this. I thought that this was one of the big driving issues for a firmware update so I find it odd it's not in included.