SpaceX's debut today will be one of the biggest waves yet in a deluge of new stock that's starting to hit the market.

Why it matters: A jump in stock issuance could tilt supply-demand dynamics that have quietly supported the market for much of the past two decades.

The latest: Fresh data from the Federal Reserve yesterday showed $389 billion in new equities hit the market during the first quarter.

• If not for the flurry of stock and SPAC issues that hit the frothy COVID-era market in early 2021, it would have been the largest single quarter of issuance on Fed records going back to 1996.

Fun fact: In fact, the only quarter that would have come close would have been the first quarter of 2000, when the dot-com boom peaked — just before all the air came out.

What they're saying: "Today's equity market faces one of the biggest shifts in supply we have seen in some time," Bob Elliott, the chief investment officer of asset manager Unlimited Funds, wrote in a recent post in his Substack, Nonconsensus. "Buybacks led by cash-producing mega-cap tech are slowing and issuance is surging with the new IPOs and secondary issuance from existing names like Google."

• "Record U.S. equity issuance will not derail the bull market in 2026," Goldman Sachs U.S. equity analysts wrote earlier this week, adding that "supply remains modest relative to the size of the equity market."

Between the lines: As everything seems to be lately, the burst of new stock is AI-related.

• The market has been shrinking for years, in part, because American corporations have embraced stock buybacks as an efficient way to return cash to shareholders.
• Cash-rich tech giants have long been some of the biggest buyers in the market.
• Now, some of those same companies are spending billions of dollars on the AI buildout, with capital expenditures burning through their free cash. (See Oracle's results late Wednesday, which the market panned.)
• Oracle said it would likely sell more stock next year. And others, like Alphabet, are also planning to sell large amounts of stock to raise cash for their AI plans.

What's next: Enormous, psychologically important IPOs from Anthropic, OpenAI and, of course, Elon Musk's SpaceX.

• Headlines suggest there's strong demand for access to these deals.
• But that could change fast, especially if SpaceX shares have trouble getting off the launchpad.

SpaceX shares are set to start trading today, and what to expect is anyone's guess: There's no such thing as a typical Day 1 for an initial public offering.

Why it matters: This one will be the biggest IPO of all time, raising $75 billion and minting thousands of new millionaire SpaceX employees — and potentially the world's first trillionaire in Elon Musk.

Follow the money: Sometimes when a stock debuts, its price "pops," as happened with Figma, Airbnb and DoorDash, as you can see in that chart.

• Seems cool, but many would argue that it's actually a sign that the company didn't price its shares properly: It sold too cheaply.
• Investors who were able to get shares at the offer price won big, but the company, well, not so much.
• Plus, ordinary investors — "retail" — who are salivating for this IPO, often don't get that early bite of stock and wind up having to buy on the open market after the initial pop and don't see a benefit.

Reality check: The first day isn't necessarily that important.

• Look at what happened back in 2012 to Facebook — its IPO was legendarily disastrous.
• Technical glitches delayed its debut and created confusion among traders. The only reason the stock didn't end down for the day is because the company's underwriters propped it up.
• In the long run, of course, lots of folks who held on got rich. Now called Meta, the company is among the most valuable in the world.

The bottom line: Hype meets reality later today when SpaceX starts trading in the public market, but the company's story is only just beginning.