According to the authors the harness isn't ARC-AGI specific though https://x.com/agenticasdk/status/2037335806264971461
This seems like an arbitrary restriction. Tool-use requires a harness, and their whitepaper never defines exactly what counts as valid.
Anyway, searching both in ARC-AGI's paper and website and directly on kaggle, I failed to find a with-harness leaderboard; can you please give the link?