Robinhood stock surged 7.4% premarket after S&P Dow Jones Indices said it will replace Caesars Entertainment in the S&P 500 on September 22. With a nearly $90 billion market cap, Robinhood's addition ensures index-tracking funds load up on shares, expanding investor reach. Retail sentiment turned bullish, as traders see upside similar to Palantir's gains post-induction.