You get a copy of the other bot's source code and are allowed to analyze it. All bots have 10,000 instructions per turn, and if you run out of time the round is negated (both players score 0 points). There is a standard function for spending X instructions evaluating a piece of quoted code

I assume that X is variable based on the amount of quoted code you're evaluating; in that case I would submit "tit for tat, defect last 3" but obfuscate my source code in such a way that it took exactly 10,000 instructions to output, or make my source code so interdependent that you'd have to quote the entire thing, and so on. I wonder how well this "cloaked tit-for-tat" would go.