SPYM, which now holds over $170.5 billion in assets, has attracted investors seeking identical S&P 500 exposure at a significantly lower cost. The fund's open-end structure also allows for immediate dividend reinvestment and securities lending, providing a slight edge over the older SPDR S&P 500 ETF Trust (SPY), which is structured as a unit investment trust. While SPY remains the most liquid equity product, favored by traders for its options market, SPYM, along with Vanguard's VOO and iShares' IVV, are increasingly preferred by long-term buy-and-hold investors. SPYM was also named the default investment for the new "Trump Accounts" on July 1, though most of the year's inflows occurred prior to this.