The Mega IPO Wave: SpaceX, OpenAI and Anthropic Are Rewriting the Index Rulebook

Every bull market has its symbols. In the late 1990s, it was the internet IPO. In 2020 and 2021, it was the SPAC, the meme stock and the zero-rate growth company. In 2026, the symbol may be something bigger: the trillion-dollar private company finally coming public.

SpaceX, OpenAI and Anthropic are not normal IPO candidates. They are the apex companies of the current cycle: artificial intelligence, commercial space, satellite infrastructure, compute, defence, consumer software, enterprise automation and founder-led technological ambition.

Their listings are likely to be among the largest and most scrutinised in market history. But the more interesting story is not simply that these companies are coming public. It is that parts of the public-market infrastructure appear to be adapting around them.

Index rules, fast-entry mechanisms, free-float requirements and retail access channels are all becoming part of the story. That matters because these companies are not arriving as ordinary new listings. They are arriving as private-market giants, already valued like the largest listed companies in the world, but potentially with very limited free float.

For index investors, this is no longer just a curiosity. It is a portfolio-construction issue.

SpaceX: the first live test case

SpaceX has now crystallised the scale of the coming wave.

The reported IPO terms are extraordinary: $135 per share, 555.6 million shares and approximately $75 billion of gross proceeds. At a reported valuation of around $1.75 trillion, this would be the largest IPO ever attempted and would immediately place SpaceX among the largest companies in the US market.

But the most important number is not the headline valuation. It is the float.

On a simple offering-size-to-valuation calculation, $75 billion of shares against a $1.75 trillion valuation represents only about 4.3% of the company. Depending on the precise definition of freely tradeable listed shares, some reports point to a somewhat higher initial free-float figure, but the conclusion is the same: this is a mega-cap company entering public markets through a narrow keyhole.

That is the market-structure problem. A company can be enormous by total market capitalisation, but relatively scarce in terms of the shares actually available to buy. That scarcity matters for price discovery, for passive flows, for volatility and for index inclusion.

SpaceX is therefore not just an IPO. It is a stress test for the modern index system.

Who are these companies?

SpaceX is a commercial space, launch and satellite infrastructure company. Its core businesses include reusable rockets, Starlink satellite broadband, Starship, national-security launch, satellite manufacturing and, following its closer integration with AI infrastructure ambitions, a broader compute and data-centre narrative.

The investment case is that SpaceX is not simply a rocket company. It is a vertically integrated infrastructure platform: launch, connectivity, satellites, defence, data and potentially orbital computing.

The risk is that investors are being asked to value not only what exists today, but several markets that remain speculative. Starlink appears to be the most economically important asset today. Launch is strategically valuable but capital intensive. Starship, orbital compute and broader space infrastructure are potentially enormous options, but they are still options.

OpenAI is the company behind ChatGPT, its API platform, enterprise AI tools, coding products and an expanding ecosystem of agents and applications. It has one of the strongest consumer technology brands in the world and has become a core platform for developers and enterprises.

The opportunity is vast. If AI becomes a new operating layer for knowledge work, OpenAI could sit close to the centre of that stack. But the capital requirements are equally vast. Frontier model development, inference, data centres, chips, safety work and distribution all require capital on a scale that makes even large private rounds look temporary.

Anthropic is the company behind Claude. Its pitch is subtly different from OpenAI’s. It is more enterprise-led, more safety-led and increasingly associated with coding, workflow automation and high-value professional use cases.

Anthropic may be seen by public investors as a cleaner enterprise AI story: less consumer spectacle, more corporate adoption. The risk is valuation. Its private-market re-rating has been so extreme that public investors may be asked to underwrite many years of flawless execution from day one.

The private-market IPO has already happened

The public IPO is not where price discovery begins. For these companies, most of the re-rating has already happened in private markets.

SpaceX has moved from roughly $150 billion in mid-2023 to around $210 billion in mid-2024, then to a reported $800 billion valuation in late 2025, before the current IPO discussion around $1.75 trillion. From the 2023 valuation to the current IPO target, that is more than an elevenfold increase. From the 2024 level, it is more than eight times. Even from late 2025, the proposed IPO valuation is more than double.

OpenAI has followed a similarly dramatic path. It was valued at around $157 billion in late 2024 and most recently raised capital at an $852 billion post-money valuation. That is more than five times higher in less than two years.

Anthropic has been even more striking. It was valued at $61.5 billion in March 2025, $380 billion in February 2026 and $965 billion in May 2026. From March 2025 to May 2026, that is nearly sixteen times higher. From February to May 2026 alone, the valuation rose by more than 150%.

These are valuation changes, not public-market returns. But they tell us something important. These companies are not being handed cheaply to public investors at the start of their growth journey. Much of the valuation uplift has already accrued in private markets.

Public investors are arriving late. That does not mean the stocks will necessarily be poor investments. But it does mean the entry valuation matters enormously.

Why list now?

There are four obvious reasons.

First, the capital requirements are immense. AI and space infrastructure are among the most capital-intensive growth opportunities in the world. Training frontier AI models, running inference at global scale, building data centres, securing chips, launching satellites, developing reusable rockets and funding orbital infrastructure all require huge amounts of capital.

Second, existing investors need liquidity. Venture funds, sovereign wealth funds, strategic investors, employees and early backers have been locked into these companies for years. The private-market model has allowed companies to stay private for longer, but that also delays distributions. IPOs turn paper valuations into liquid securities.

Third, public shares are strategic currency. They can be used for acquisitions, compensation, partnerships and balance-sheet flexibility.

Fourth, and most importantly for index investors, public listings unlock benchmark demand. Once a company becomes eligible for major indices, passive and benchmark-aware investors become structural buyers. That does not guarantee returns, but it changes the demand curve.

The index-rule story: this is the real issue

Index investors often think they are avoiding active decisions. In reality, they are outsourcing active decisions to index methodology.

That is the key point.

Index providers are not passive observers. They write the rules that define what “the market” is. Those rules determine whether a company enters an index, when it enters, how much of it index funds must own, and how quickly passive capital must buy.

Historically, IPOs had to meet seasoning, liquidity, free-float and sometimes profitability requirements before entering major indices. That made sense when companies generally listed earlier in their lifecycle, at smaller valuations and with more conventional shareholder structures.

But SpaceX, OpenAI and Anthropic break the old model. They are already mega-caps before listing. They may come public with limited free floats. They may have short public trading histories. Some may not meet traditional profitability tests. Yet if they are excluded for too long, indices risk looking incomplete or unrepresentative.

This creates a tension. Ignore them and the index may fail to reflect the public market. Include them too quickly and passive investors may be forced into illiquid, low-float, highly valued stocks.

Different index providers are now resolving that tension differently.

Nasdaq: adapting quickly

Nasdaq has made the clearest change.

Its updated Nasdaq-100 methodology creates a faster route for very large IPOs. A newly listed company can be assessed shortly after trading begins and potentially added to the Nasdaq-100 far sooner than would previously have been possible, provided it is large enough and meets the relevant requirements.

This is not designed for ordinary IPOs. It is designed for companies that are already large enough to sit near the top of the index on day one.

The second important change is float. Nasdaq has removed the minimum free-float requirement for Nasdaq-100 eligibility. That matters enormously for companies like SpaceX, where the headline market capitalisation may be vast but the freely tradeable portion of shares may be small.

Nasdaq has not ignored the liquidity problem. Instead, it has introduced a modified weighting approach. For low-float companies, index weight is constrained by a cap linked to free float. In simplified terms, the index can include the company but limit the amount of market capitalisation that counts for weighting purposes.

That is the compromise. The company is not excluded simply because of low float, but it is not weighted as though every share is freely available either.

The clean interpretation is that Nasdaq is modernising its index methodology for a market where companies stay private longer and list at much larger sizes.

The more cynical interpretation is that the rulebook is being adjusted just in time for the largest private companies in the world.

Both interpretations can be true.

S&P 500: holding the line, for now

The S&P 500 position is especially important because it has changed from the earlier market discussion.

S&P Dow Jones Indices did consult on potential changes for MegaCap companies. Those proposals included reducing the IPO seasoning period, relaxing minimum investable-float requirements and creating an exception to the usual financial-viability test.

However, S&P has now decided not to make those changes for the S&P 500, S&P MidCap 400 or S&P SmallCap 600.

That means SpaceX, OpenAI and Anthropic do not currently get a special fast-track route into the S&P 500 simply because they are enormous. The existing hurdles remain: seasoning, investable float and, crucially, profitability.

This is significant. SpaceX reported a net loss in 2025, which matters because S&P 500 eligibility is not just about size. It is also about financial viability.

But S&P did make narrower changes elsewhere. It adjusted eligibility rules for broader market indices, including the S&P Total Market Index, the S&P Completion Index and the Dow Jones U.S. Total Stock Market Index. Those indices are designed to represent the broader investment universe, so S&P has been more willing to adapt there than in its flagship large-cap benchmark.

That actually strengthens the article’s central point. The rulebook is not changing uniformly. Nasdaq and some broad-market index families are adapting quickly. S&P 500 has, for now, refused to bend.

Passive investors therefore need to understand not only that they own “an index”, but which index methodology they are relying on.

FTSE Russell, MSCI and the broader response

FTSE Russell has also moved toward faster treatment for very large IPOs. Its updated framework allows eligible IPOs to enter after a short trading period, while also allowing some flexibility around minimum free-float or voting-rights requirements where certain conditions are met.

MSCI has indicated that it will apply its existing early-inclusion framework for large IPOs, which could also bring SpaceX into global benchmarks relatively quickly if size and free-float thresholds are met.

The pattern is clear. Some index providers are adapting. Others are holding the line. The result is that two investors who both believe they own “the US market” could end up with very different exposure depending on whether they own Nasdaq-100, S&P 500, Russell, MSCI, FTSE Russell or total-market products.

That is not a trivial difference. It is an active allocation decision disguised as passive investing.

Retail access: the other side of the same story

There is another market-structure angle: retail access.

Fidelity has said SpaceX IPO participation may be available to customers with as little as $2,000 in a retail brokerage account. That is far lower than the usual six-figure thresholds often associated with IPO eligibility. The reason given is that SpaceX has reserved a much larger percentage of the offering for retail investors than is typical.

This is worth noting. The SpaceX IPO is not only being prepared for institutions and index funds. It is also being opened more widely to retail investors.

That has a positive interpretation: broader access, more participation and less of the upside being reserved for private-market insiders.

It also has a cautionary interpretation: retail demand may be used as part of the distribution mechanism for an enormous, highly valued, low-float IPO.

Again, both interpretations can be true.

What should investors expect from performance?

The near-term performance could be powerful. A large IPO, limited float, intense retail interest, institutional demand and potential index inclusion are all supportive technical factors.

SpaceX also has scarcity value. Public investors have wanted access to it for years. If the IPO is oversubscribed, and if index demand follows, the first phase of trading could be extremely strong.

But the medium-term question is different. A great company can still be a poor investment if the valuation already assumes too much. At $1.75 trillion, SpaceX would be valued like one of the greatest companies in the world before public investors have had much time to assess the business under public-market scrutiny.

The same applies to OpenAI and Anthropic. These may be exceptional companies, but their private valuations already discount enormous success. The risk is not that the businesses are irrelevant. The risk is that the market capitalisation is already capitalising years of future dominance.

In practical terms, investors should separate the company from the stock. The company may be extraordinary. The stock may still be vulnerable if the starting price is too high.

Is this a market top?

People are asking that question, and they should be.

The bearish argument is straightforward. Mega IPO waves often arrive when private owners believe public markets will pay premium prices. The timing is rarely accidental. If insiders, private investors and companies can raise capital or create liquidity at peak enthusiasm, they have an incentive to do so.

The dot-com comparison is obvious: transformational technology, enormous addressable markets, aggressive valuations, retail excitement, index demand and a willingness to price future markets that barely exist today.

SpaceX adds another twist. If the IPO is heavily primary issuance, that is less obviously a simple insider cash-out. But the valuation still matters. A mega-cap listing with limited free float requires public investors to accept a very high mark based on a relatively narrow traded supply.

AI adds a second warning sign. Anthropic and OpenAI have seen valuation increases that would normally be associated with public-market mania, not private funding rounds. Those valuations may ultimately be justified, but the burden of proof is high.

The counterargument is also important. These are not empty-shell companies. SpaceX has real launch capability, a global satellite network and strategic defence relevance. OpenAI has global distribution and one of the strongest software brands in the world. Anthropic has meaningful enterprise traction and reported revenue growth. Unlike many bubble-era IPOs, these companies are not merely concepts.

So is this a market top?

Not necessarily. But it is a late-cycle signal.

The better framing is this: the market is being asked to absorb enormous future expectations at once. When the highest-profile private companies all seek public capital at extreme valuations, while some index providers and retail platforms adapt to accommodate them, investors should pay attention.

That does not mean sell everything. It means stop pretending this is normal.

What are the positives?

There are genuine positives.

First, access. Public investors have been largely shut out of the most important private companies for too long. If the strongest businesses stay private until they are worth hundreds of billions or even trillions, public markets lose some of their purpose. Listings by SpaceX, OpenAI and Anthropic would reopen access, even if late.

Second, transparency. Public companies must disclose more: revenue, margins, customer concentration, capital expenditure, related-party transactions, governance, risk factors and share-based compensation. That transparency is healthy.

Third, capital formation. Successful mega IPOs would unlock liquidity for venture funds, sovereign investors, employees and early backers. That money can be recycled into the next generation of companies.

Fourth, benchmark relevance. If indices refuse to include the largest and most important public companies indefinitely, they become less representative. Index providers are not wrong to recognise that the market has changed.

Fifth, innovation exposure. AI and space infrastructure may be genuinely transformative. If even part of the bull case proves right, these companies could become central to the next phase of productivity, communications, defence and computing.

The bottom line

SpaceX, OpenAI and Anthropic are not just IPO stories. They are market-structure stories.

SpaceX’s reported terms make the issue unavoidable: a $75 billion IPO, a valuation around $1.75 trillion and a limited initial free float. That is not a normal listing. It is a mega-cap entering public markets through a narrow keyhole.

That is why index rules matter.

Nasdaq has adapted quickly, creating a faster route for very large IPOs and changing how low-float companies can be treated. S&P considered similar accommodation for MegaCap companies in the S&P 500, but ultimately refused to change the flagship index’s rules. FTSE Russell and MSCI have their own frameworks, which may allow earlier inclusion in some benchmarks.

This is not a secret conspiracy. It is an open market-structure debate.

The old rulebook was not built for trillion-dollar private companies with limited free float. Some index providers are rewriting the rulebook around them. Others are holding the line.

For passive investors, the lesson is clear: passive does not mean neutral.

If you own an index, you own a rulebook. And when the rulebook changes, so does your portfolio.

This article is for information only and does not constitute investment advice or a personal recommendation. Capital is at risk, and the value of investments can fall as well as rise.