Morgan Stanley: S&P 500 Falls 5% on Equal Weight, AI Concentration Risk Accumulates Before Year-End According to Deep Tide TechFlow, Morgan Stanley's research report dated October 9, 2026, points out that the S&P 500 index fell 0.5% in September in terms of market capitalization weight, and 5% on an equal weight basis; the top six contributing stocks contributed approximately 190 basis points, while the remaining constituent stocks dragged down the index by approximately 240 basis points; the median forward P/E ratio for AI and semiconductor stocks is approximately 32 times, higher than the average of approximately 19 times over the past ten years. Morgan Stanley believes that the AI rally is still supported by earnings, but concentration risk is accumulating. It recommends selectively holding AI positions, gradually reducing thematic concentration, tactically increasing positions in low-volatility stocks, and allocating to financially sound value stocks to prepare for a possible turning point from December to early 2027. https://www.techflowpost.com/zh-CN/newsletter/139635
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大摩：标普等权重跌 5%，AI 集中度风险在年末前积累 深潮 TechFlow 消息，据潮向研究，摩根士丹利 2026年 10月 9 日研报指出，标普 500 指数 9 月市值加权下跌 0.5%，等权重口径下跌 5%；前六大贡献股合计贡献约 190 个基点，其余成分股合计拖累约 240 个基点；AI 和半导体股中位数远期市盈率约 32 倍，高于过去十年均值约 19 倍。 大摩判断，AI 行情仍受盈利支撑，集中度风险在积累。建议有选择地持有 AI 仓位，逐步降低主题集中度，战术性加仓低波动股，并配置财务稳健价值股，为 12 月到 2027 年初的可能转折做准备。 https://www.techflowpost.com/zh-CN/newsletter/139635