How the SpaceX IPO makes index funds less diversified

SpaceX filed its confidential registration statement with the SEC on April 1, 2026, setting the stage for what could be the largest IPO in history. The company is targeting a $1.75 trillion valuation and a raise of up to $75 billion, with a June listing on the Nasdaq. Those numbers alone rewrite the record books. But for the millions of Americans who invest through index funds, the SpaceX IPO raises a question that deserves more attention than it gets: what happens to your diversification when a company this massive enters the index?

The answer involves a problem that has been building for years. The S&P 500 is already more concentrated than most investors realize, with just 10 companies accounting for roughly 40% of the entire index. Adding SpaceX and other mega-cap IPOs could make it worse.

Why S&P 500 concentration risk matters to you

Most people think of the S&P 500 as a diversified investment. Five hundred companies across every major sector of the American economy. In theory, that is exactly what it is. In practice, the index’s market-cap weighting means that the biggest companies carry the most influence over your returns.

Today, the top 10 stocks make up roughly 38% of the index. Nvidia alone holds a weighting of over 7%, which Apollo’s Torsten Slok has identified as the largest single-stock weight since the data began in 1981. If you invest $1,000 in an S&P 500 index fund, about $400 goes into just 10 companies, while the remaining $600 gets spread across the other 490.

That is not what most people picture when they hear “diversified.”

Apollo Chief Economist Torsten Slok has described the situation bluntly: the S&P 500 “basically doesn’t offer much diversification anymore.” The structure creates a self-reinforcing cycle. Passive inflows disproportionately support the largest stocks, increasing their weights and reinforcing their performance leadership regardless of fundamentals. Money flows in, weights go up, and the index becomes more concentrated, which means more money flows to the same few companies.

The problem is not that these are bad companies. Many of them earn their valuations through strong profits and competitive advantages. The problem is structural. When a handful of stocks dominate the index, a single earnings miss or regulatory action at one company can drag down the entire benchmark. An earnings disappointment at Nvidia, which alone represents nearly 8% of the index, would hit the portfolios of every passive investor in America.

How SpaceX could deepen the problem

SpaceX will not qualify for the S&P 500 right away. The index requires a 50% public float for inclusion, and SpaceX is expected to debut with a float of only 3-8%, as Elon Musk maintains tight control through a dual-class share structure. But according to The Wall Street Journal, SpaceX’s advisers have already approached major index providers to discuss accelerated inclusion. When it eventually qualifies, the mechanics get interesting.

At a $1.75 trillion valuation, SpaceX would rank among the six or seven most valuable public companies on Earth. It would be larger than Meta. When index funds eventually add it, they do not raise new cash. They sell existing holdings to buy the new entrant. That forced rebalancing can create selling pressure on existing mega-cap holdings, which in turn can trigger momentum strategies to pile on further selling.

And SpaceX is not alone. OpenAI is targeting a potential IPO valuation of $1 trillion, and Anthropic recently raised $30 billion at a $380 billion valuation. Slok has projected that if all three companies go public and join the S&P 500, the top 10 weighting could approach 50%. Half of every dollar in your index fund would go to just 10 companies.

A different kind of IPO

There is something else worth considering about these mega IPOs. They represent a fundamentally different proposition for public market investors than the tech IPOs of previous generations.

When Google went public in 2004, it debuted at a $23 billion valuation. Today, Alphabet is worth over $3.5 trillion. Public market investors who bought at the IPO captured enormous value as the company grew. Facebook’s 2012 IPO valued it at $104 billion, which seemed eye-popping at the time. Meta is now worth well over $1 trillion. Even with Facebook’s rocky start, early public investors who held on multiplied their money many times over.

SpaceX, by contrast, has grown from a $46 billion private valuation in 2020 to a $1.75 trillion IPO target in 2026. That is roughly 38 times growth in six years, all captured by private market investors. Public investors buying at $1.75 trillion are arriving at a very different point in the company’s growth story than those who bought Google at $23 billion or even Facebook at $104 billion.

That does not mean SpaceX cannot grow further. It might. Starlink’s subscriber base is expanding rapidly, and the space economy holds real long-term potential. But it does mean the risk-reward profile looks different from the IPOs that built the current mega-cap pantheon. Investors should consider whether a $1.75 trillion entry point leaves adequate room for upside, especially given the capital intensity of rocket launches, satellite deployment, and deep-space ambitions.

There is also the question of fundamentals. Google was already profitable at its IPO, earning roughly $1 billion on $3.2 billion in revenue in the year before it went public. Facebook had $1 billion in earnings on $3.7 billion in revenue at the time of its listing. SpaceX’s full financials remain confidential until the S-1 goes public, so investors cannot yet evaluate whether the company’s earnings justify a $1.75 trillion price tag. That uncertainty alone is worth taking seriously.

Hidden AI exposure through the back door

The SpaceX IPO adds another wrinkle that many investors may overlook. In February 2026, SpaceX completed an all-stock merger with xAI, Musk’s artificial intelligence venture. The combined entity now bundles rockets, satellite internet, and AI under one corporate umbrella.

This matters for concentration risk because the S&P 500 is already heavily exposed to AI. The Magnificent Seven stocks that dominate the index all have significant AI operations or AI-driven growth narratives. Unlike past periods when top stocks spanned unrelated industries, today’s leaders are closely linked by a common AI theme. Slok has noted that S&P 500 investors “remain overexposed to AI.”

Adding SpaceX-xAI to the index would layer even more AI exposure onto portfolios that already have plenty of it. Investors who think they are diversifying into aerospace and satellite technology would also be taking on a significant AI bet. If AI spending disappoints or the broader AI narrative reverses, the correlated drawdown across index holdings could be severe.

What investors can do about SpaceX IPO concentration risk

None of this means you should panic or sell your index funds tomorrow. Index investing remains one of the most accessible and cost-effective ways to participate in the stock market over the long term.

But it does mean that the S&P 500 may not be providing the diversification many investors assume. With concentration at historic highs and the potential for mega IPOs to push it higher, it is worth asking whether your portfolio matches your actual risk tolerance.

Some investors address this by supplementing index funds with equal-weight strategies, which assign the same weight to every company rather than letting the largest ones dominate. Others look to international diversification or sector-specific funds that avoid overweighting technology.

Another approach is individual stock selection with a focus on business fundamentals and valuation. By owning companies based on what they earn rather than how large they already are, investors can build portfolios that do not blindly follow the index into ever-higher concentration. This requires more research and discipline, but it offers something that cap-weighted index funds increasingly do not: genuine diversification tied to business quality rather than market momentum.

At Magnifina, this is exactly how we approach investing. We specialize in individual stock portfolios built around business fundamentals and disciplined valuation. If you are wondering whether your current portfolio carries more concentration risk than you realize, we would love to help you find out. Answer 4 quick questions to see if we’re a good fit.