I made my agent more capable and it got worse

Builder Journal · ARC Prize 2026 There is a moment in every role-playing game where you load your character with so much heavy gear that they can barely walk. Strongest sword in the game, can't reach the fight. I did the machine-learning version of that this month. I kept making my agent more capable, and the scoreboard kept punishing me for it, and it took me two tries to understand that the upgrades were the problem. A quick frame, in case this is your first entry in this thread : I'm in the ARC Prize 2026, building an agent that has to learn small games it has never seen, with no instructions. As the benchmark's creator measured it, the hardest part by far is the piece that figures out the rules of a game by experimenting on it. So that piece is where I have been pouring my effort. The obvious upgrade The obvious way to make that piece better is to teach it more kinds of games. If it can model three families of puzzle today, teach it a fourth, and it should win more. So I did exactly that. I built support for a new class of game it could recognize and solve, wrote it carefully, tested it, and confirmed the thing I wanted to confirm: the agent now beat a game it provably could not beat the day before. Real, verified, new capability. Not a story I was telling myself, a genuine new skill on the board. Then I submitted, and the score went down. Twice This is the part I want to be honest about, because one bad result is noise and two is a pattern. My agent's attempts to use this theory-building component had already been underwhelming on the real board, landing around 0.05, 0.07, and 0.09 across earlier tries, all of them under the 0.25 my plain, careful agent scores when it does not reach for the fancy component at all. The fourth skill was supposed to turn that corner. Instead the next submission came in at 0.04, the worst of the lot. I had added ability and the number had dropped, again. So I stopped adding and started counting. I ran a survey across twenty-five of