One small step for man, one giant leap for the financial markets. That seems to be the current theme at the moment, with financial publications and non-industry news alike, all clambering for any new details on three very prominent (and imminent) initial public offerings (IPOs). Whilst IPOs are rarely dull affairs, Anthropic, OpenAI and SpaceX are potentially some of the most influential we have seen in market history. The sheer publicity surrounding these companies is potentially overwhelming, but what truly makes these IPOs so special, and what portfolio impact may they cause?
Most of the excitement surrounding these listings is from the sheer size of the companies launching their IPOs. Fittingly for a company looking to further space exploration, SpaceX has set astronomical heights for its IPO. When looking at other large US IPOs, SpaceX is likely to have the highest valuation of any major offering on record (1) at $75 bn, surpassing Alibaba’s record $22bn listing in 2014 (2). Anthropic has filed a confidential IPO, which means there is slightly less information available on the company compared to SpaceX. However, Anthropic recently raised $65bn in funding, placing its value around $965bn (3), breaching the $200bn threshold to be classed as a mega-cap stock. OpenAI has just filed its respective confidential IPO and sits at a rough valuation of $852bn (4). Next to Anthropic and SpaceX, this may seem relatively small, but this IPO is still historically large and has already caused excitement from its filing on the 8th June.
Some of the fanfare is the possible early inclusion and adoption of these mega-cap stocks into indexes. All providers, like the FTSE Russell, S&P Dow Jones and NASDAQ, have rules surrounding what securities can qualify for inclusion in their specific index. Due to the sheer potential market capitalisation of these companies when they IPO, indexes have had to review their inclusion policies to see whether securities inclusion will be expedited. Some indexes have confirmed the fast-track entry of SpaceX (and likely Anthropic and OpenAI), including FTSE Russell. If we consider SpaceX, with a valuation of up to $1.75trn (5), this market capitalisation well exceeds the provider’s inclusion rules and will likely be included in their indexes in as little as a week after listing.
However, other providers are not set for early inclusion, and it may be a year or longer before these mega-cap listings make it onto S&P indices. S&P Dow Jones indices have rather stringent entry requirements that previously blocked Musk’s Tesla from index inclusion when it was first listed. These include a 12-month seasoning period in which companies have to post profits in their most recent quarter, as well as for the sum of their most recent four quarters. As SpaceX posted a loss of $4.94bn in 2025, this would mean it is not eligible for inclusion in the index (6). Index inclusion is far from automatic, so it is worth understanding what index you have exposure to in your portfolio in order to know what exposure to these mega-cap stocks you can expect early on.
These IPOs can seem daunting to those who are reading the speculation online, but it's important to consider how this will actually impact investor portfolios. Market capitalisation and company size are only one aspect of a much more complex story. Whilst both Anthropic and OpenAI have not disclosed how much they are looking to raise from their offerings, we know that SpaceX is seeking to raise $75bn. Whilst the market capitalisation of SpaceX may make it look like an intimidating prospect for index funds, it’s important to understand that most index funds are based on ‘float-adjusted market capitalisation’. This simply means that the position size within the fund is based not on the market capitalisation of the company as a whole, but rather on the value of the shares available for the public to buy. SpaceX, whilst receiving much fanfare surrounding the IPO, is only expected to float 5% of its shares, meaning its inclusion in a global index would be relatively small compared to some expectations.
Putting this into perspective, if you invested £10,000 in a global index fund and assumed SpaceX, Anthropic and OpenAI each floated only 5% of their shares, the combined exposure to these three companies could be around £17.
Chart and figures for illustrative purposes only. Actual results will vary.
Weights based on 5% assumed free-float vs ~£100trn FTSE All-World free-float market cap. Figures rounded; illustrative only, not advice.
Sources: SpaceX $1.75trn IPO target (Reuters / Capital.com, Jun 2026); OpenAI $852bn (Bloomberg / OpenAI, Mar 2026); Anthropic $965bn (Tracxn, May 2026); FTSE All-World free-float methodology (FTSE Russell / LSEG).
Free-float adjusted indexes do not allocate capital based on potential ‘hype’ around a security, but rather based on market-determined weights based on an investable reality. Rather than passing judgment on whether a particular IPO will succeed or fail, they simply follow rules and take the market as it is. This approach is pivotal as it allows investors exposure to companies based on economic reality, rather than market narratives. This translates to the actual impact on portfolios likely being modest at first, with representation that aligns with what is available to the wider markets. Below we have compared the various market capitalisations of SpaceX, Anthropic and OpenAI vs. the actual, or speculated, investable free-float of these companies.
Chart and figures for illustrative purposes only. Actual results will vary.
Headline values: SpaceX $1.75trn (IPO target), Anthropic $965bn, OpenAI $852bn.
Investable = free-float cap. SpaceX ~5% reported; *Anthropic and OpenAI floats not yet disclosed, 5% free-float assumed.
Holding shown vs ~$105trn FTSE All-World free-float market cap (2026 approx.). Figures rounded. Illustrative only, not advice.
Sources: SpaceX $1.75trn IPO target (Reuters / Capital.com, Jun 2026); OpenAI $852bn (Bloomberg / OpenAI, Mar 2026); Anthropic $965bn (Tracxn, May 2026); FTSE All-World free-float methodology (FTSE Russell / LSEG).
The other consideration is understanding how previous record-breaking IPOs impacted various indexes upon their inclusion. Saudi Aramco IPOed in December 2019 and currently holds the record for the largest IPO on record at $29.4bn (7). Much like SpaceX, this initial offering was actually only a fraction of its massive $1.7trn market valuation. What was the actual impact on index fund holders? Marginal at most. In the MSCI Emerging Markets index, it accounted for 0.5% of the weighting, which is impressive, but really had little tangible impact on index fund holders. (8) When you take a look at this inclusion on a global index like the MSCI All Country World Index (MSCI ACWI), the impact is even further diluted. Aramco had an initial weighting of roughly 0.06%, meaning a fractional change to the composition of the index. (9) Whilst this had some notable press at the time, this seems to have been forgotten in the circus of the upcoming mega-IPOs. Taking a look at the historical impact of large IPOs and their actual impact on investor portfolios is a useful way to help keep grounded in reality rather than getting caught up in the escalating fanfare.
There is also often discourse on the underperformance of IPOs after the initial frenzy. It is a well-researched phenomenon that IPOs can underperform (Ritter, 1991) general markets (10). In Reuters’ recent research, they found that investors would have been better off buying the S&P 500 index than investing in 50 IPOs with the highest valuations of the last 5 years. But it’s worth pointing out that this isn’t always the case, and that sometimes this underperformance can be short-term noise. From Reuters’ same research, Arm Holdings, which IPOed in 2023, actually outpaced the S&P 500, returning 403% compared to 71% for the index. Meta also provides a great case study, with its stock falling almost 50% in the first few months after offering. Meta now sits at roughly $1.59 trillion, illustrating that poor early returns do not always equate to a security being a long-term poor investment. It is important to note that past performance is not a reliable indicator of future results. Therefore, it is nearly impossible to know which company IPOs are the ones that will reshape industries and buck the underperformance trend. The best advice to follow may well be John Bogle, the pioneer of index investing: “don’t look for the needle in the haystack. Just buy the haystack!”.
Whether you love or loathe the rise of these mega-cap stocks, they are likely to impact markets. As with any security, there are risks to inclusion in a portfolio, but there is also a lost-opportunity risk from not including these stocks. For those who are worried about these securities, broad market diversification may be your best bet. The key takeaway is, like all things investing, it’s important to have a solid foundation of an investment philosophy you trust and believe in. A philosophy built on evidence and empirical research and a rules-based approach can help keep portfolios focused on the longer-term goals.
1) Reuters, How SpaceX stacks up against some of the biggest US IPOs, 2026: https://www.reuters.com/legal/transactional/how-spacex-stacks-up-against-some-biggest-us-ipos-2026-05-15/
2) CNBC, Retail investors will get access to SpaceX’s IPO—here’s what to know before buying, 2026: https://www.cnbc.com/2026/05/21/spacex-ipo-what-retail-investors-need-to-know-before-buying-shares.html
3) Bloomberg, Anthropic Eclipses OpenAI With Valuation of $965 Billion: 2026https://www.reuters.com/legal/government/spacex-set-fast-entry-into-us-global-indexes-under-new-ftse-rules-2026-05-26/
4) Bloomberg, OpenAI Valued at $852 Billion After Completing $122 Billion Round, 2026: https://www.bloomberg.com/news/articles/2026-03-31/openai-valued-at-852-billion-after-completing-122-billion-round
5) Reuters, SpaceX set for fast entry into US, global indexes under new FTSE rules, 2026: https://www.reuters.com/legal/government/spacex-set-fast-entry-into-us-global-indexes-under-new-ftse-rules-2026-05-26/
6) Reuters, SpaceX blocked from early US benchmark index entry as S&P reaffirms existing rules, 2026: https://www.reuters.com/business/finance/sp-global-keeps-fast-entry-proposal-unchanged-spacex-listing-looms-2026-06-04/
7) Reuters, Saudi Aramco raises IPO to record $29.4 billion by over-allotment of shares, 2020: https://www.reuters.com/legal/transactional/spacex-debut-draws-crowd-few-recent-hot-ipos-outpace-market-2026-05-26/
8) Morningstar, Aramco won't have much impact on major indexes. Here's why., 2019: https://sg.finance.yahoo.com/news/invested-us-10-000-meta-060000344.html
9) Morningstar, Aramco won't have much impact on major indexes. Here's why., 2019: https://sg.finance.yahoo.com/news/invested-us-10-000-meta-060000344.html
10) J.R. Ritter, The long-run performance of initial public offerings, J. Finance, 46 (1991), pp. 3-27: https://www.reuters.com/article/business/saudi-aramco-raises-ipo-to-record-294-billion-by-over-allotment-of-shares-idUSKBN1ZB03C/
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