I spoke with a Canon Rep today at an unrelated event, and he confirmed it does support continuous focus tracking of moving subjects.
He suggested for the best performance one should use lenses with Stepping motors, but it might work with USM lenses as well.
Canon EOS C100 firmware 22.214.171.124
Canon EOS C100 Cinema EOS Camera
Firmware Version 126.96.36.199.00 incorporates the following additional functions and modifications:
A function has been added which allows automatic continuous focusing and iris setting on a subject in the center of the screen when using the EF-S18-135mm f3.5-5.6 IS STM lens.
The polarity of the XLR terminal has been modified to improve compatibility with external audio devices. The pin configuration has been modified to be consistent with the Instruction Manual.
For details about the new functions, please download the latest version of the C100 User Manual (PDF) .
Firmware Version 188.8.131.52.00 is for EOS C100 cameras with Firmware Version 184.108.40.206.00. If the camera's firmware is already Version 220.127.116.11.00, it is not necessary to update the firmware. Once the camera is updated to the latest version, it cannot be restored to a previous version.
The new Firmware Version 18.104.22.168.00 can be downloaded by clicking here.
This information is for residents of the United States and Puerto Rico only. If you do not reside in the USA or Puerto Rico, please contact the Canon Customer Support Center in your region.
If you have not already done so, please register your Canon EOS C100 Cinema EOS Camera. By registering, we will be able to notify you via email about future service upgrades.
Customer Support Operations
Additional report of improvements!
OK I downloaded it and installed it on the C100 just before the camera left our building and did some very quick tests using the 18-135mm STM lens. The AF in Focus Lock mode was very fast and smooth. Much better than before.
AF in Continuous mode (which is accessible as a setting in the camera menu) is fully continuous which means it keeps focusing without any interaction.
The One Shot (focus lock) AF mode still requires you to push the Focus button on the front of the camera body.
In my initial test, I was very impressed with the speed and smoothness of the Continuous Focusing. It was very good in very low light, and would probably be even better in good light. It seemed to track a moving person diagonally very well, which is not easy for most contrast detection systems.
Canon U.S.A., Inc.
(cover photo credit: snap from the video)