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The oldest exchange-traded fund listed in the U.S. was just toppled in terms of assets under management by a Vanguard ETF that more cheaply tracks the S&P 500 index.

The SPDR S&P 500 ETF Trust SPY, launched in 1993 as the first U.S. ETF, has swelled to slightly more than  $630 billion in assets under management based on share count on Tuesday and net asset value on Feb. 14, according to calculations from Aniket Ullal, head of ETF research and analytics at CFRA Research. But that now trails the Vanguard S&P 500 ETF VOO, which has about $1.5 billion more in assets, at almost $632 billion, to become the world’s largest exchange-traded fund, he found.

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Both funds track the S&P 500 index SPX , but they appeal to different types of investors.

The SPDR S&P 500 ETF Trust is popular with institutional traders, including those who might be looking to make options-related trades tied to the ETF, while the Vanguard fund tends to attract individual investors with a buy-and-hold strategy for their portfolios, according to Ullal.

The success of the Vanguard S&P 500 ETF in gathering assets reflects the established trend of increasing adoption of exchange-traded funds by individual investors, he said, but the SPDR S&P 500 ETF Trust “still has a very important place as an institutional product.”

Individual investors have been attracted to the Vanguard fund’s lower cost, according to Ullal.

The expense ratio of the Vanguard S&P 500 ETF is just 0.03%, a lower fee compared with the SPDR S&P 500 ETF Trust. The SPDR fund has an expense ratio of 0.0945%, according to data on the website of State Street Global Advisors.

The SPDR S&P 500 ETF Trust attracts large, sophisticated investors who are actively trading the fund and historically have been drawn to its low bid-ask spreads, said Ullal. Meanwhile, ordinary investors as well as wealth managers have looked to less expensive options for core exposure to the U.S. stock market, he said.

For example, the third-largest exchange-traded fund in the U.S. is the iShares Core S&P 500 ETF IVV, which many financial advisers turn to on behalf of their clients, according to Ullal. That fund has around $609 billion of assets under management based on its share count as of Tuesday and its net asset value as of Feb. 14, CFRA calculated.