Earlier quoted context omitted.
> An Engine requires rules as well. Yes, the basic rules of chess.
If that's the only rule, it can quickly become "who can spend more on compute on a single game" championship. Not very interesting.
The teams submit their binaries to the organizers beforehand, and the organizers run them on the tournament hardware.
There are some questions beforehand about what hardware to use (for example, some engines use GPUs and others don't), but after that is settled, the tournament is run in a fair way, hardware-wise.