The ex-AI index is a compilation of all the stocks in the S&P 500 that are not related to AI, also referred to as old-economy stocks. Typically, you buy an index because it's diversified, but the AI trade and its impact on the market caps of the top stock in the S&P has made the index concentrated on the tech theme. However, an index that drops that theme entirely could be a way to give investors the diversification they're craving.