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2/2 At their peak last week, AI stocks were 49% of the S&P 500 (chart). This is the most concentrated the stock market has been on a single theme since the railroad stocks of the late 19th century. Higher when SpaceX, Anthropic, and OpenAI are added, after they are all public. Given this historic concentration, and AI and non-AI stocks are moving opposite each other (above), is the stock market effectively two asset classes * AI * Everything Else