The euphoria toward artificial intelligence is creating a strange kind of new math in the stock market: Plans for massive AI investments often lead to even larger increases in market value for the companies writing the checks.

Take Nvidia Corp., which last week said it will buy a $5 billion stake in rival Intel Corp. and on Monday announced plans to invest up to $100 billion in ChatGPT creator OpenAI. The chipmaker added more than $320 billion in market value in the three trading days when the plans were announced — triple the amount the company is expected to spend under both agreements.

Then on Wednesday, Alibaba Group Holding Ltd.’s US shares jumped as much as 10% after the company said it would spend even more on AI than a $50 billion target set earlier in the year. While the total a

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