SpaceX is about to be in your 401(k) whether you like it or not.

It was the biggest I.P.O. ever, dethroning Saudi Aramco, Saudi Arabia’s state-owned oil company, which was valued at $1.7 trillion and raised more than $29 billion when it went public in 2019. SpaceX raised $75 billion from its offering, more than the combined amount amassed by every other U.S. I.P.O. over the past two years, according to Renaissance Capital, a research and advisory firm.

The pop in SpaceX’s share price also catapulted Mr. Musk, 54, to become the world’s first trillionaire. The entrepreneur, who not only leads SpaceX but also runs the electric carmaker Tesla and other businesses, has long been the planet’s wealthiest person. But passing the trillionaire milestone is significant, further augmenting Mr. Musk’s fortune and influence.

The offering also enriched a coterie of Mr. Musk’s friends and venture capital and private investment firms. Thousands of SpaceX employees also instantly became millionaires.

Mr. Musk spent Friday at the company’s headquarters in Starbase, Texas, where he celebrated with employees, family, friends and investors. “It is certainly hard to believe that a little company that started in a warehouse in El Segundo is now going public,” he told them, referring to SpaceX’s founding in 2002 in Southern California.

A SpaceX spokesman and Mr. Musk did not return requests for comment.

SpaceX’s blockbuster I.P.O. paves the way for mega offerings by the A.I. start-ups OpenAI and Anthropic, which are each valued at nearly $1 trillion. Never have three trillion-dollar entities gone public in the same year. Their stock market debuts could signal that a new era of corporate power has arrived, with SpaceX, OpenAI and Anthropic joining the pantheon of tech giants like Google, Microsoft, Amazon, Nvidia, Apple, Netflix and Meta.

For SpaceX, the first day of trading capped a long road. Mr. Musk founded the company 24 years ago with the idea of making humans a multiplanetary species. For years, his dreams of private spaceflight seemed to be out of reach.

But Mr. Musk has remade the space race with partly reusable rockets and transformed communication with the company’s satellite internet service, Starlink. In February, SpaceX bought his A.I. company, xAI, which owned the social media platform X, creating a conglomerate of the tech billionaire’s various interests.

Mr. Musk has used SpaceX as a kind of piggy bank over the last two decades, securing loans from the company to himself and relying on the firm to shore up several troubled businesses in his orbit. That was enabled partly because of Mr. Musk’s iron grip on SpaceX; he controlled around 85 percent of the shareholder votes before the I.P.O. because of a class of supervoting shares and other corporate structures.

In its I.P.O., SpaceX sold more than 555 million shares, representing a little more than 4 percent of the company’s outstanding stock. The company and its bankers courted traditional institutional investors and encouraged wealthy individuals and retail investors to buy. SpaceX also wanted several indexes to change their rules so that its shares would be included faster than normal, which would eventually compel managers of large index funds to buy up the stock.

SpaceX’s stock price is expected to swing higher and lower in the weeks after its listing, not necessarily because of shifting opinions about the company but because of certain technicalities. SpaceX is expected to face high demand for its relatively low number of shares available, potentially leading to sharp price rises. That could change as investor enthusiasm dies down and more shares become available to trade.

JPMorgan analysts said this week that the recent average I.P.O. share price increase stood at 32 percent after the first day of trading, but fell to a loss of 26 percent after 12 months.

Daniel Hanson, a portfolio manager at the investment firm Neuberger Berman who oversees a fund with a $200 million investment in SpaceX, said the speed at which SpaceX went public — six months from when Mr. Musk first announced his intentions — was an example of its executive team’s “tenacity.”

“It’s exciting to see the team recognized by the public for what they have accomplished since their founding 24 years ago,” he said.

In recent weeks, SpaceX, which has contracts with NASA and other federal agencies, has also faced questions about its business, including its spending and how it can justify its valuation. In its I.P.O. prospectus, the company reported that it had lost more than $4.9 billion last year, compared with a $791 million profit in 2024 because of increased expenditures on A.I. Revenue was $18.7 billion last year, up 33 percent from the previous year.

In contrast, Meta, which owns Facebook, Instagram and WhatsApp, is valued at slightly less than SpaceX at just over $1.4 trillion, though it pulls in far more revenue and generates large profits. Last year, Meta’s revenue totaled $201 billion, and profit was $60.5 billion.

SpaceX has said it plans to use the money it raises from its I.P.O. to pay off loans and fund various moonshots, including Mr. Musk’s goals of putting A.I. data centers into orbit, building a lunar factory and eventually sending humans to Mars.

While skeptics have questioned whether these plans are feasible, Mr. Musk’s fans abound. In New York, an excited crowd of several dozen people gathered outside the Nasdaq building in Times Square on Friday morning, including Zach Boucher, 45, who flew in from California overnight to see SpaceX listed on the Nasdaq.

Mr. Boucher said he was buying more than 2,200 SpaceX shares through Wells Fargo and was “never going to sell, I’m holding for the long term.”

This moment is “like getting in on the ground floor of GE or GM, or being here when Microsoft opened,” he said.

Goldman Sachs, Morgan Stanley, Bank of America, Citigroup, JPMorgan Chase and 18 other banks served as underwriters for SpaceX’s I.P.O.

(The New York Times has sued OpenAI and Microsoft, claiming copyright infringement of news content related to A.I. systems. The two companies have denied the claims.)

Joe Rennison and Lauren McCarthy contributed reporting from New York.