Private equity giant Blackstone Inc. is the latest addition to the S&P 500 Index, the first alternative asset manager to join the equity gauge. Airbnb Inc. is added as well.

The New York-based Blackstone and Airbnb will replace Lincoln National Corp. and Newell Brands Inc. prior to the start of trading on Sept. 18, S&P Dow Jones Indices said in a press release late Friday.

Shares of Blackstone, the world’s largest alternative asset manager, were up 4.1% in after hours trading while Airbnb’s rallied about 4%.

Wall Street analysts had predicted that Blackstone would be added to the S&P 500 after an April decision by S&P Dow Jones to drop a 2017 rule that barred corporations with multiple share classes from index membership. Blackstone has a dual share structure with unequal voting rights.

To qualify for the S&P 500, companies must be highly liquid US firms with a market capitalization of at least $14.5 billion, and meet profitability, liquidity and share-float standards. As of July 5, thresholds for the S&P MidCap 400 Index and S&P SmallCap 600 Index are $5.2 billion to $14.5 billion and $850 million to $5.2 billion, respectively.

Additions and removals to the S&P 500 often but not always happen when the index is rebalanced each quarter. They can also occur at other points of the year, like after mergers and acquisitions. S&P Dow Jones makes these adjustments to account for shifts in market capitalizations and, on occasion, to adjust for the market’s gyrations.

Inclusion in the benchmark gauge is becoming more important for companies in a world increasingly dominated by passive investment funds. Furthermore, a spot in the coveted S&P 500 boosts a firm’s investor profile and adds to trading liquidity — factors that can potentially propel a company’s stock price higher.

Last week, Kenvue Inc, the maker of Tylenol and Listerine, replaced Advance Auto Parts Inc. in the S&P 500. The move came after Kenvue’s record split-off from Johnson & Johnson.

Read more: J&J’s Kenvue Swap Opens Door to Arbs, Longs and Index Funds

Meanwhile, Lincoln National and Newell Brands were removed from the S&P 500 Index. Expulsion from the benchmark can weigh on stock prices, as passive investors are forced to sell the shares and realignment with the S&P 500’s new composition.

--With assistance from Alexandra Semenova and Jessica Menton.