For agent harness I did Claude Code, Codex, Grok Build. This was primarily a cost driven decision — I have a lot of free tokens and I didn't want to pay API prices for this.
For game harness I used minimal BW-API issue command and get observation apis as tools. I felt this was the most fair way to do it on my small scale.
In the future I would like to integrate code mode and multiple games/I think if it was a best of 5 where each agent could learn from its past games and build its own automations over time that would be much more interesting.
Or possibly even whether they can learn from a game themselves. "Analyse your game for your failures" -> Then give a fresh agent of the same model that "learnings" doc for the next match. Do the rankings change over time, if models can write instructions for future selves?