How is SG for SPX negative but positive for SPY? SPY and SPX are different trading instruments and have different options positions. Related articles What is the SpotGamma Gamma Index? What is Bookmap? Is negative call gamma bullish? In terms of risk on/off how do we interpret different Vol Triggers for SPY/SPX and QQQ/NDX? How does Next Exp Delta & Gamma effect the price going into that expiration and on Monday?