Nearly $800 billion in market capitalization vanished from the Magnificent Seven in a single trading session on July 23, 2026 — a staggering number that reframes what was supposed to be a routine earnings week into a stress test for the entire AI investment thesis. The US stock market decline that followed wasn’t just a bad day for two companies. It exposed a fault line that investors have been quietly dreading: what happens when the bill for the AI buildout finally arrives, and nobody can say when the returns will show up?