It’s hard to overstate the significance of the soaring stock prices of artificial intelligence companies to the economy. Spending by well-off Americans, driven by their surging stock portfolios, is the single most significant driver of growth. This so-called wealth effect is responsible for nearly half a percentage point of real GDP growth over the past year, accounting for one-fourth of the economy’s overall growth. The wealth effect has been a tailwind to growth, more or less, since recovering from the Global Financial Crisis. Of course, housing wealth is also up a lot, and the well-to-do are still holding onto a big pile of cash that they accumulated during the pandemic shutdowns. But given the outsize gains in wealth compared with the growth in incomes and the economy more broadly – household net worth is now eight times after-tax income, compared with an average of 5.5 times in the decades between WWII and the GFC – it is prudent to consider how sustainable this is. And if it isn’t, what does it mean for future growth?