The post-IPO story of SpaceX is entering its most critical chapter. As locked-up shares gradually become unlocked and the public float ratio climbs rapidly, forced buying pressure from passive funds is building up—Goldman Sachs' latest estimates show that the Russell 1000 Growth Index rebalancing on December 11 alone could trigger more than $10.9 billion in passive buying demand.
According to an analysis by Goldman Sachs U.S. equity strategist Ben Snider in the latest edition of "US Weekly Kickstart," SpaceX's public float ratio has surged from about 5% at IPO to roughly one-third. Since major indices generally use free-float market capitalization weighting, the continued expansion of tradable shares will push SpaceX's weight in major indices ever higher, in turn triggering mandatory purchases by passive funds. As of the end of October, ETFs collectively held approximately $32 billion in SpaceX stock, a sharp increase from $11 billion at the end of June.
The market significance of this rebalancing lies in the fact that passive funds will be on the buy side, while unlocking shareholders—primarily insiders—will be on the sell side. Looking further ahead, the window for inclusion in the S&P 500 is approaching, at which point the benchmark asset base of nearly $12 trillion will come into play, while SpaceX's current weight in that index remains at zero.
Rapid Float Expansion, Passive Holdings Follow Suit
At the time of SpaceX's IPO, only about 5% of shares were available for trading, leading major index providers to almost entirely ignore the company when calculating weights. This situation is changing rapidly.
Snider noted that roughly one-third of SpaceX shares are now included in the public float, and based on the existing lockup expiration schedule, the float ratio is expected to rise to approximately 50% by mid-2027, "consistent with historical precedents of low initial floats in large IPOs."
The direct result of float expansion is a corresponding increase in passive fund holdings. Goldman Sachs data shows that as of the end of October, various ETFs collectively held approximately $32 billion in SpaceX stock, representing 1.4% of its total market capitalization, compared to just $11 billion and 0.5% at the end of June. Of that, about $20 billion came from funds tracking the Nasdaq 100 Index.
Notably, the Nasdaq 100 Index adjusted its methodology earlier this year—for constituent stocks with a float ratio below 33%, weights are calculated at three times the float market capitalization; once the float ratio exceeds 33%, it switches to full listed market capitalization. This means the index has already absorbed most of the impact from float increases in advance, and Snider therefore concludes that "the continued increase in SpaceX's float will have a relatively limited mechanical impact on the Nasdaq 100."
December 11: Russell Rebalancing Becomes the Biggest Focus
What truly deserves market attention is the regular rebalancing of the Russell 1000 Growth Index. Goldman Sachs estimates that if rebalancing were conducted immediately based on currently unlocked shares, SpaceX's weight in the index would jump from the current 0.2% to 1.5%.
Based on a benchmark scale of approximately $800 billion, this weight change would force approximately $10.9 billion in passive buying. Goldman Sachs explicitly marked the timing: "The next regular rebalancing of the Russell 1000 Growth Index is on December 11."
The scale of other indices is relatively limited: Nasdaq 100 rebalancing is expected to bring about $1.4 billion in demand, with the S&P Total Market Index and MSCI ACWI each contributing approximately $500 million.
The "Index Doomsday" Has Not Arrived
At the time of the IPO, the market widely feared that SpaceX's inclusion in indices would distort concentration, valuations, and passive fund flows. Snider's data shows that these concerns largely did not materialize.
Excluding SpaceX, the Nasdaq 100's price-to-earnings ratio only dipped slightly from 19.5 times to 19.2 times; sales growth declined by about 1 percentage point; and index returns since inclusion showed almost no difference (including SpaceX at -10.3%, excluding at -10.0%). Even concentration metrics changed only marginally—the top ten constituents account for roughly 50% of the index weight regardless.
Snider compared it to Tesla's inclusion in the S&P 500 in 2020—another inclusion event that drew intense market attention at the time, but whose actual impact on index valuations ultimately proved negligible. His conclusion is that SpaceX's impact on "stock index performance, concentration, and valuations is far smaller than many investors had previously expected."
The fundamental reason is that the mere 5% float ratio at IPO always limited the actual scale of its impact on indices.
Who Holds SpaceX, Who Will Become Sellers
As passive funds begin to enter in force, the market also needs to pay attention to the supply structure on the sell side.
Goldman Sachs estimates that as of the end of June, insiders and related parties collectively held approximately 68.8% of SpaceX shares, worth about $1.56 trillion; hedge funds held about 3.3%, and mutual funds held less than 1%. Another approximately 26.5% (worth about $600 billion) is held by parties not required to publicly disclose, which Goldman Sachs believes "primarily corresponds to individual investors."
Snider noted that lockup arrangements and the trend of moderate passive holding growth indicate that "insiders and individual investors still hold the majority of SpaceX shares."
This means the passive buying from the December 11 rebalancing will primarily face insider shareholders who are gradually unlocking and waiting to cash out. This tug-of-war between buyers and sellers will be the first real stress test for observing SpaceX's price movements after large-scale float expansion.
S&P 500 Inclusion: Second Half of 2027 May Be the Window
Currently, SpaceX's weight in the S&P 500 Index, which has a benchmark scale of $11.9 trillion, remains at zero.
There are two obstacles: the S&P 500 requires a company to have been publicly listed for 12 months and to have achieved GAAP profitability in the most recent quarter and on a combined basis over the past four quarters. According to market consensus, SpaceX is expected to meet the profitability threshold only after its second-quarter 2027 earnings are released, by which time the 12-month listing requirement will also be satisfied simultaneously—based on this calculation, the inclusion window points to the second half of 2027.
Snider also mentioned another potential path: if SpaceX engages in a merger with an existing S&P 500 constituent, the index committee will review eligibility changes "on a case-by-case basis," potentially accelerating the inclusion process.
Once included in the S&P 500, it will face passive fund pressure of an entirely different magnitude. At that point, the tension between forced buying and the supply from continuously unlocking insider shareholders will be far more complex than the December Russell rebalancing.
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