Robinhood was included in the S&P 500 index, but Strategy's stock price fell nearly 3% after the market closed due to its omission.

Michael Saylor's MSTR was unexpectedly omitted from the S&P 500, sending its stock price down 3% after hours. Robinhood, on the other hand, was unexpectedly included, sending its stock price up 7%. The adjustment takes effect on September 22nd.