(These are the market notes on today's action by Mike Santoli, CNBC's Senior Markets Commentator. See today's video update from Mike above.) In my weekend column , I cited the recent run of partnerships in the semiconductor and data-center realm as "signaling to investors the danger of calling the top in AI enthusiasm." On cue, Nvidia and OpenAI unveiled what they said is a $100 billion investment in AI capacity, sending Nvidia and related stocks flying and more than offsetting the fatigue evident in the broader market. Entering the week with the S & P 500 at a record high and moderately overbought, in what is statistically the weakest week of the calendar, the market's rotational alacrity and the brute force of megacap-tech momentum were enough to lift the index nearly half a percent even

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