AI stocks vs dot-com bubble: CAPE at 38, concentration above 2000 levels, but companies are actually profitable

The Shiller CAPE ratio sits at 38-40, second only to the dot-com peak of 44.19, and S&P 500 top-10 concentration now exceeds year-2000 levels by nearly 50%. However, unlike dot-com era companies, today's AI leaders are massively profitable — Nvidia alone earned $120B in net income, and the tech sector trades at 30x forward earnings versus 50x in 2000. The central unresolved question is whether $660-690 billion in annual hyperscaler capex will generate returns that justify the investment. Bulls point to real earnings growth (Nasdaq-100 up 19% YoY) and committed cloud revenue backlogs; bears highlight OpenAI's $852B valuation with no profits, retail euphoria, and the historical precedent of fibre-optic companies that built real infrastructure but went bankrupt anyway. The bubble question cannot be answered until the AI infrastructure cycle produces results.