With each change to the S&P 500, the index that dominates becomes a bit more like the digital world that dominates daily life.

Take the latest update: Come tomorrow, Interactive Brokers Group (IBKR) will join the broad market measure, taking the place of drugstore operator Walgreens Boots Alliance (WBA), which is set to be taken private by Sycamore Partners later this year. Shares of Interactive Brokers, which were recently creeping higher, are up roughly 40% year-to-date. (Talen Energy (TLN) will take Interactive Brokers's spot in the S&P MidCap 400.)

Interactive Brokers will be the third fintech firm to join the index of the U.S.'s largest companies this year, following Coinbase Global (COIN) and Block (XYZ). While the company was incorporated in the 1990s, its roots go back to the late 1970s when founder Thomas Peterffy started to explore algorithmic trading. Peterffy and his engineers famously hacked the Nasdaq terminal to enable automated trading in 1987, and circumvented the exchange's manual entry rules by building a robot with rubberized fingers that would type in trades into a keyboard.

These days, Interactive Brokers is a soup-to-nuts broker-dealer with desktop and mobile apps that enable investors to trade securities, derivatives, currencies, commodities, crypto, and as of last year, event contracts in prediction markets. Rivals include E-Trade, Schwab (SCHW), and Fidelity.

Walgreens, meanwhile, will soon be a private company for the first time in almost 100 years. The company agreed to a deal worth roughly $10 billion after struggling to revive sales and amid thinning profit margins that led to a spate of store closures.

Its decline started in the last decade as its business model was caught between a rock—the rise of big-box and digital retailers like Walmart (WMT), Target (TGT) and Amazon (AMZN)—and a hard place, with drug intermediaries lowering disbursement rates on prescriptions.

Interactive Brokers has a market cap around $28 billion, according to Visible Alpha data.