What US mega-cap IPOs mean for investors

Mega-cap IPOs are unlikely to disrupt US equities immediately, but their scale shows that investors increasingly need access to private markets to capture economic growth.

• SpaceX, OpenAI and Anthropic have a combined valuation above USD 4,000 billion, yet index inclusion will be gradual because benchmarks use free float rather than total market capitalisation; SpaceX initially floated about 4% of its shares, later rising to 36%.
• Among the 10 largest IPOs from 2010 to 2025, J.P. Morgan Research finds that average free float increased from around 45% on day one to around 80% six months later, while lock-ups typically delay sales by 90 to 180 days.
• Index-entry rules also limit the immediate effect: FTSE, MSCI and Nasdaq allow fast entry after a handful of trading days, whereas S&P Global requires 12 months of trading before S&P 500 eligibility.
• SpaceX stayed private for 24 years before listing in June 2026 at a USD 1,770 billion valuation, compared with Amazon’s IPO valuation below USD 1 billion, Google’s roughly USD 40 billion and Meta’s around USD 151 billion.
• The median technology company now reaches the public market at age 12, versus less than six years in the late 1990s, and generates almost three times the revenue at IPO; Anthropic’s May 2026 Series H raised USD 65 billion at a USD 965 billion valuation.
• Bain reported that 86% of US companies with revenues above USD 100 million were still private in 2023, while public equity markets had almost 30% fewer companies than in the late 1990s.

Takeaway: The immediate supply effect of mega-cap IPOs should be limited, but public-only portfolios risk missing an increasing share of early value creation; investors should consider both public and private markets, while recognising that the profitability of AI investments remains unresolved.