Index funds now steer mega-IPOs like SpaceX and Anthropic

Anthropic's upcoming IPO, expected to begin trading next week, will see its early share price driven by forced index-fund buying rather than organic demand, mirroring SpaceX's June debut. The AI firm aims to raise up to $64.4 billion, valuing it at $1.4 trillion. Major index providers like Nasdaq have rewritten inclusion rules, ensuring Anthropic joins at least six big indexes within 5 to 15 days of listing, triggering roughly $19 billion in passive demand from tracking funds. SpaceX's successful debut saw shares surge 50% by day three, driven by index inclusion, retail allocation, and option-related hedging. Anthropic's trajectory may differ slightly as employees can sell shares on day one, and it has a separate $26 billion private sale without lock-ups. The new dynamics have created lucrative opportunities for index-rebalancing funds, with SpaceX serving as a blueprint for mega-share debuts.