Several websites are reporting that the new firmware for the Canon 5Diii are now available through unofficial channels. Apparently someone sent a camera in to Canon and they returned it with the new firmware on a thumbdrive and the user decided to share.
Canon has officially announced it: Canon 5Diii Firmware Update 1.2
The firmware will:
1. Allow for clean HDMI out (some are reporting that there is no audio with this feature)
2. Allow for better focusing when shooting with extenders.
3. Fixes AF Assit Speed with a Speedlite