Stay Grounded on Moonshot IPOs

The impending SpaceX initial public offering (IPO) has some investors looking for a liftoff in their index funds and ETFs—even as others brace for potential volatility.

While Vanguard’s index products will purchase shares in SpaceX in the days and weeks following the IPO launch, we will take a more grounded approach. Investors should understand that index rules, which govern the Vanguard products that seek to track them, will require a measured incorporation of stock from any new public company.

Investors should be reminded that in addition to diversification, low costs, and transparency, one of indexing’s core principles is to let markets, not hype, settle the outcomes.

What it means: Companies’ weight in indexes, and thus index products, is based on the value of the companies’ shares that are available for public investors to buy (referred to as the “float adjusted capitalization”), not the companies’ headline valuation, which includes shares privately held by insiders and other select investors. As a result, the stock of SpaceX, and other “hot” IPOs, will make up only a small portion of index funds initially, and they will only receive a greater portion over time once more shares become available to the public.

• For example, while SpaceX’s potential valuation is reported to be more than $1 trillion, its weight in any index that includes it will initially be based on around 5% of its shares being available to the public.

Why it matters: While mega IPOs will be added to many broad indexes relatively quickly, index funds allocate based on what’s available to the public (“the float”), not restricted or closely held stock owned by management, employees, or major shareholders.

The bottom line: Vanguard has long advocated for low-cost, diversified investing and disciplined, rules-based index construction. We believe faster index inclusion for IPOs enables indexes to remain representative of, and evolve with, the IPO market, which is positive for investors. Still, for most index-based portfolios, the impact of SpaceX, Anthropic, OpenAI, or any hot IPO may initially be modest.

Here are three key points to review:

• Index rules keep IPO volatility from overwhelming portfolios. Indexing is designed to reflect the market and provide broad diversification rather than respond to short-term IPO dislocations. While fast-track inclusion keeps indexes representative, float adjustments can help limit outsized allocations and mitigate the impact of large IPO inclusions.
• New index rules do allow investors to participate more quickly. Most large index providers now allow inclusion of mega IPOs soon after they start trading, instead of waiting for months or more, or requiring a larger initial float size, as was previously the standard. But new IPOs are not added to indexes on day one. Even with the “fast-track” inclusion policies for very large IPOs offered by some index providers, index rules still set a minimum waiting period before the stock is added, usually within 5 to 15 trading days. One exception: S&P has decided to adhere to its current rules in its S&P 1500 Composite Series (including the S&P 500), which require a company to be profitable in its most recent quarter as ​well as for the sum of its most recent four quarters.
• Market-weighting avoids undue concentration in any single name. Because these large IPOs represent a relatively small share of the company’s overall size—expected to be less than 5% in the case of SpaceX—they typically represent a modest share of an index. As early investors, founders, and employees sell additional shares in the months after an IPO, the company’s free float expands—and its weight in float-adjusted indexes can rise organically.

Changes for Vanguard ETFs

The resulting Vanguard portfolio changes for SpaceX are expected to be limited, as portfolio weights are anticipated at first to be 1% or less. That should help keep turnover and tax impact low with little change to portfolio tracking.

Here is how quickly some Vanguard ETFs will include SpaceX and the other IPOs:

Source: Vanguard.

New inclusion rules for mega IPOs

New inclusion rules to allow swifter adoption of mega IPOs have been adopted by most major providers. Some providers (like CRSP, FTSE, and Russell) emphasize speed and breadth, while S&P takes a more cautious, qualitative approach, and Nasdaq’s strategy is to capture very large tech listings quickly with less concern about initial float. All approaches remain rules-based frameworks to reinforce fairness, predictability, and alignment with what’s realistically investable for fund holders.

Comparison of major index providers’ IPO inclusion approaches

Source: Vanguard as of June 8, 2026.