Anthropic’s targeted $2 trillion IPO valuation, with marketing eyed for early November and a potential debut before Thanksgiving, underpins its slim lead in the 2026 largest-IPO-by-market-cap market at 51.8% implied probability versus SpaceX’s 44.5%. SpaceX’s June offering priced at $1.77 trillion—the largest U.S. IPO on record by proceeds—established a high bar that Anthropic seeks to surpass despite trailing in 2025 revenue and posting a $42 billion net loss against heavy non-cancelable compute commitments. Traders weigh Anthropic’s rapid run-rate expansion toward $65 billion annualized against execution risks and index-inclusion flows, while SpaceX’s diversified Starlink and launch revenue provide a more established base. OpenAI’s deferral to 2027 and limited prospects for other candidates reinforce the binary contest centered on Anthropic’s pricing outcome.