When SpaceX launched its initial public offering (IPO) on June 12th it raised $75 billion and was valued at more than $2 trillion within a week. This made it one of the largest companies in the world, and Elon Musk the world’s first trillionaire.
The size of the offering is remarkable on its own. What matters more for your portfolio is what happens to the market indexes when a company that large arrives all at once.
The IPO of SpaceX is interesting because of how it, and the IPOs of OpenAI and Anthropic which are expected later this year, may affect the broader stock market. SpaceX was immediately one of the largest public companies in the world. It was added to the Russell 1000 index in late June and the Nasdaq-100 in July. It will likely be added to the S&P 500 in June 2027.
Source: JP Morgan, July 2026
This matters in two ways. The first is mechanical. A large amount of money moves into these new companies as they are added to index funds, simply because of their size. That pushes up the stock price in the short term for reasons that do not necessarily have to do with the company’s business and earnings.
The second effect is more lasting. Each addition of this size makes the index itself more concentrated. So the equity index that serves as a proxy for “the market,” whether it be the S&P 500 or the Russell 1000, is increasingly tied to the success of a handful of very large, mostly technology-related companies.
The S&P 500 is already at its highest concentration in 50 years, with the largest companies representing roughly 38% of total market value.
One of the defining characteristics of today’s technology industry is that many of the largest companies are both competitors and major customers and suppliers of one another. The relationships are highly intertwined, even when the companies compete strongly in some areas. If these companies fail to perform as expected, the effect on the broad market will be much larger than in the past.
The response is not complicated, but it does have to be deliberate. A portfolio matched to your goals and risk level needs holdings that are not participating as heavily in the tech-driven returns that increasingly make up U.S. index returns. International, small company, and value-focused positions all serve that purpose.
If you hold a broad U.S. index fund, it is worth looking at what is actually inside it. The label has not changed in 50 years, but the contents have. Knowing how much of your portfolio sits in a few large technology companies is the first step in deciding whether that is the exposure you want.