High-Stakes Earnings Season Puts AI Stocks to the Test

The market's most expensive stocks, measured by forward price-to-earnings ratios at the end of the second quarter, suffered unusually sharp valuation contraction in the third quarter, according to Trivariate Research. Their multiple compression was roughly 100 times as large as that of the cheapest names, an extreme seen only 5.3% of the time since 1999. AI capital-spending-sensitive high-valuation names such as AMD, Marvell, Corning and Bloom Energy were hit hardest. The S&P 500's forward price-to-earnings ratio fell to 19 at the end of last week from 22 at the start of 2026.