Interactive Brokers (IBKR) surged 4.7% premarket after being added to the S&P 500, replacing Walgreens Boots Alliance, which is going private. Inclusion draws passive fund inflows, boosting investor demand. Robinhood (HOOD), still excluded despite a $96 billion valuation, slipped 0.7%. Traders stayed bullish on IBKR but bearish on HOOD, though some expect its index entry later this year.