Stripe's secondary-market marks have climbed to approximately $180–184 billion as of early October 2026, supported by expanding payment volume, AI-agent commerce initiatives, and the OpenRouter acquisition, narrowing the gap with American Express's roughly $205 billion market capitalization. Traders see the December 31 outcome as finely balanced because Amex's established card network and recent share-price softness contrast with Stripe's faster private-market repricing and growth trajectory. Key swing factors include Amex's October 23 earnings release, which could shift its valuation, ongoing Stripe secondary trading activity, and broader macroeconomic influences on consumer spending and interest-rate expectations that affect both companies' multiples.