The S&P 500 Month-End futures settle based on the official S&P 500 Index closing price at 4:00 p.m. ET on the final business date of the month. Trading is available both on-screen and off-screen via a central limit order book and privately negotiated block trades. American-style options are offered, allowing for flexibility in exercising and targeting the month-end closing index price for option positions.

Read more at CME Group: Managing Month-End Equity Flows and Portfolio Risk