The financial markets experienced significant volatility on September 20, 2024, due to the largest September expiry of all time, with $4.5 trillion in notional value set to expire. This event, known as 'Quadruple Witching,' occurs quarterly and involves the simultaneous expiration of stock index options, stock options, stock index futures, and single stock futures. Goldman Sachs has warned of an imminent 'Gamma Flip,' indicating potential market instability. Additionally, index-tracking funds are set to reshuffle $250 billion of shares, adding to the market's volatility. Traders are bracing for further fluctuations as the S&P 500 gamma turns negative, suggesting Wall Street dealers may not buy the dip to maintain neutral positioning. The expiry includes $2.6 trillion in SPX Sep regular options, and there are seven sessions left in Q3.