This is the summer of the mega-IPO, a flood of new stock listings after years of drought.

Mine is not a personal finance column, but there’s never been a moment quite like this. The opportunity to invest at a relatively early stage of an industry, artificial intelligence in this case, doesn’t come often.

And the dollars these companies are raising from investors far exceed what we saw the last time this happened, during the social media era about 15 years ago.

Individual investors focused mainly on retirement may be surprised to learn they have become part of the action even if they didn’t choose to be.

That’s because these huge new stock listings — we’ve already had SpaceX, and Anthropic and OpenAI will follow — have been granted a shortcut into some indexes and investments tied to them.

The biggest, the S&P 500, is sticking to its rule that companies must be publicly traded for at least a year before they are included in the index. But the CRSP U.S. Total Market Index has already incorporated SpaceX, and some others soon will.

When it comes to your own money, it’s best to be a bit skeptical about what you hear, maybe even cynical. The cynical take on this tide of IPOs is that companies and their underwriting banks are spreading risk while offering only a modicum of control to new investors — and that early valuations are detached from financial reality.

The optimistic view is the chance to profit from the next turn of the crank in high technology, which is the development and proliferation of AI, is now available to everyone.

In the two weeks since the SpaceX IPO, optimism has reigned. Investors have been caught up in the future-is-AI theme — and the momentum behind it. The company instantly became one of the 10 most valuable in the world, with a market cap exceeding $2 trillion.

But stories and themes aren’t the only thing that drives value.

Stock prices are shaped by investor perceptions about four things: expectations about the future profits of companies, interest rates (stocks tend to rise when they fall and fall when they rise), money flows and what traders are forced to do (think about 2008 when institutional investors sold stocks to cover their bad bets in housing derivatives).

Money flows and what traders are forced to do are more powerful at the moment than the first two. To be sure, corporate profit growth could slow, and interest rates are already forecast to tick higher.

To think about what traders are forced to do, consider the work of someone who manages an investment fund that benchmarks to the broader market index. An index fund should be a way to manage risk, but that risk goes up when the market is dominated by relatively few mega-cap stocks. That professional manager is forced to take positions in stocks even if they know that doing so makes their fund riskier.

The term for this is “market concentration,” and it has been a hot button topic as AI and technology stocks took off over the past year or so.

Market concentration can creep up on individual investors at moments like now when the market is dominated by a hot sector. Fortunately, some personal finance tools like Quicken can show investments by industry.

And many financial advisers have tools to help their clients understand when concentration starts to emerge. Some low-fee investment services, like Betterment, offer to automatically rebalance portfolios at regular intervals.

Craig Johnson, who looks for hard-to-spot stock movements as chief technical analyst at Piper Sandler in Minneapolis, said individuals can make a habit of checking for when portfolios become too heavy in one sector or class of investment.

The question he said investors must ask: “Is that concentration appropriate to my needs?”

“Does that mean they should become technicians and try to time the market? Not necessarily,” Johnson said. “But it is OK to buy and sell.”

To give an example of how market concentration happens, technology stocks accounted for 22.5% of the CRSP U.S. Total Market Index five years ago and 33.5% as of April 30. SpaceX’s $2 trillion valuation immediately after listing gave the company a more than 1% weighting in the index of 3,700 stocks.

“Where I would encourage focus or attention is checking your account statements as well as underlying indices,” said Alex Pengelly, the 2026 chair of the board of the Financial Planning Association of Minnesota.

“For someone managing their own investments, it just requires a little bit higher level of due diligence because the index you’re using might not look like the index of five years ago or 10 years ago,” he said. “They are fluid and the rate of fluidity is higher now.”

Long ago, an investment adviser told me that stock investing is a test of one’s belief that the future will be better than today. That’s still true, but money is never free.

This summer’s mega-IPOs are a different kind of test: whether the giants of AI can make the rest of us believe they know what they’re doing.

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