The results of his blind test were that human mastering by experts got the most votes as sounding best - BUT....the top AI mastering tool is called Matchering - an open source AI mastering tool that appears to be what subscription tools are plugging into:
Yes it's a vocal remover tool but the mastering option is under the menu CHOOSE PROCESS METHOD>AUDIO TOOLS and you can select Matchering.
Then you add your track and a reference tracks and it'll do it's magic. It got better results in the blind test than Ozone's auto-mastering (although he only tested the automated version, without human tweaking, which he rated a lot higher).
So basically it's not the best possible, but it's a free version of some of the subscription based AI mastering tools - so not for everyone but certainly a useful thing to try out, especially if you're on a tight budget!