指数纳入规则是核心风险。Tesla 因 S&P 要求最近一季与连续四季获利为正而延后纳入；从 2020 年 11 月 16 日宣布纳入至 12 月 18 日正式加入，股价上涨 70%，自 3 月低点至纳入时几乎上涨 10 倍。目前约 14兆美元直接追踪 S&P 500，另有 4兆美元追踪 Nasdaq 与 Russell 1000，合计约持有美国约 80兆美元股市的近四分之一。
若 SpaceX 以 2兆美元估值出售 4% 股份，流通市值约 800亿美元，总市值相当于美国股市约 2.5%。若主要指数以完整市值权重立即纳入，指数基金可能需买入超过 5000亿美元股票，但市场仅有约 800亿美元可供交易；按自由流通量计算，需求或降至最多 300亿美元。自 2012 年以来，S&P 500 大幅跑赢 Next 500，但过去 25 年其现金流年增速约低 3 个百分点，估值溢价已升至约 80%。
A SpaceX IPO would not destroy capital markets, but it would test their resilience and intensify the valuation gap between companies inside and outside major indices. During the dotcom bubble, only a few IPOs raised more than $1bn, while Saudi Aramco raised about $29bn in 2019 at a valuation near $1.9tn. SpaceX, Anthropic and OpenAI are expected to raise roughly $170bn combined at valuations that may exceed $4tn.
Index inclusion rules are the central risk. Tesla’s S&P 500 entry was delayed by requirements for positive latest-quarter and trailing four-quarter earnings; from the November 16, 2020 announcement to its December 18 inclusion, Tesla rose 70 percent, and from its March lows to admission it rose nearly tenfold. About $14tn directly tracks the S&P 500, with another $4tn tracking the Nasdaq and Russell 1000, together owning nearly one-quarter of the roughly $80tn US equity market.
If SpaceX sold 4 percent at a $2tn valuation, its float would be about $80bn, while total market value would equal about 2.5 percent of the US market. If major indices immediately added it at full market-value weight, index funds might need over $500bn of shares against only about $80bn available; float weighting could reduce demand to up to $30bn. Since 2012, the S&P 500 has far outperformed the Next 500, despite cash-flow growth over 25 years being about 3 percentage points slower, lifting its valuation premium to roughly 80 percent.