Unique Short Title: "Silent Auctions at the Close: How Mandate Transparency and Hedging Opacity Distort End-of-Day Price Formation"

Shortened Abstract: This paper examines how institutional flow transparency shapes intraday price dynamics at market close. Using a novel dataset identifying counterparties in U.S. options and leveraged ETFs, we find that mandated, fully transparent leveraged ETF rebalancing produces short-lived momentum, quickly absorbed by liquidity providers. In contrast, opaque, discretionary hedging by options market makers creates more persistent price distortions due to information asymmetry. We show these effects reverse at different speeds—leveraged ETF impacts fade by the next open, while gamma-driven flows persist longer. Over time, ETF flow effects diminish as markets learn, but options hedging effects remain significant, highlighting how flow visibility determines market efficiency and arbitrage potential during critical closing periods.