These two popular tech stocks just got added to the S&P 500

The S&P 500 has new company... or companies, rather. And among investors, two of the three additions in this quarter's index were seen as overdue; more 'about time' than a surprise.

S&P Global announced Friday that adtech company AppLovin  (APP)  and fintech goliath Robinhood  (HOOD)  will be added to the S&P 500, replacing MarketAxess Holdings MKTX and Caesars Entertainment CZR in the index's quarterly makeover. The changes will take effect before the market opens on Sept. 22.

Investors reacted to the changes in after hours trading on Friday, with Applovin and Robinhood stock jumping 6% respectively, while MarketAxess and Caesars fell 0.5% each in extended trading.

How did AppLovin and Robinhood get here?

The high-flying names' additions to the index come after they were shrugged off by the index's selection committee multiple times. S&P Global made no changes to the world's most-watched financial club in its quarterly shakeup in June. It further subverted expectations with one-off additions of smaller tech companies like cloud monitoring service Datadog  (DDOG) , programmatic advertising company The Trade Desk  (TTD) , and delivery app DoorDash  (DASH) .

Meanwhile, AppLovin and Robinhood remained two of the index's most eligible bachelors, with their stocks ascending 455% and 414% over the past year, making them two of the U.S. market's standout stocks. Their steepening fortunes helped them become the first and third most valuable firms not already in the S&P 500, valued at $166 billion and $90 billion respectively.

In the Margins: Emcor Group

A lesser-known industrial name, Emcor Group Inc.  (EME)  also scored inclusion in the index in the forthcoming shakeup, replacing the ailing solar firm Enphase Energy  (ENPH) . Emcor stock has risen more than 77% over the past year.

Who's Next?

With just 500 spots in the heavily-watched index, the S&P 500 is one of the most exclusive clubs on Wall Street. However, each shakeup stirs discussions about which companies should (and shouldn't) have made the cut.

Notable exclusions from this quarter's big changes include bitcoin treasury company Strategy  (MSTR)  (formerly MicroStrategy), which is now the largest publicly-traded firm not in the S&P 500, with a market cap of over $95 billion.

Analysts have also singled out private equity firm Brookfield Asset Management  (BAM) , video game platform Roblox  (RBLX) , and social media company Reddit  (RDDT) , among others.