You can ignore AI giants like SpaceX, but your 401(k) won’t

While you might want to ignore all the hubbub around Space X, Elon Musk and IPOs, your 401(k) likely can’t. Space X is now worth $2.1 trillion after its stock launched 19.2% higher in its debut on Wall Street. Whether or not you believe it deserves to be worth more than Exxon Mobil, Bank of America and Coca-Cola combined, the collective market does. And if Space X maintains that big a value, it will join some high-profile stock indexes. Many of these indexes don’t care about how realistic a company’s growth plans are or who its CEO is. They’re simply trying to show how slices of the market, or the whole thing, are performing. And if SpaceX is big enough to meet the qualifications to join those indexes, whether it’s in a few weeks or a year, it will gain entry. That matters for investors and their 401(k) accounts because they’re depending more than ever on funds that simply mimic these indexes. It’s a lower-cost way to invest, allowing savers to keep more of their investments. Partly because of that, such index funds have usually proven to be better performers than funds that try to pick and choose individual stocks. Just one in five actively managed U.S. stock funds survived and beat their average index peer over the last decade, at 21%, according to Morningstar’s data through 2025. Such disparities in performance meant investors had more money invested in U.S. index funds than actively managed ones beginning in 2024, and the gap has only grown since then. Here’s a look at what’s going on: What indexes are They’re things the investment industry has created to answer the question: What is the market doing? It’s otherwise tough to answer quickly when the U.S. market has thousands of stocks moving in different directions at any moment. The S&P 500 is perhaps the most famous and influential index. It tracks 500 of the biggest U.S. stocks, and trillions of dollars in investments are either directly mimi