Analysts warn the stock market is in a late-stage bubble driven by AI investments, with Capital Economics forecasting an S&P 500 crash of 21% to 6,500 by end-2027 after reaching 8,250 this year. Key bubble indicators include extreme valuations near dotcom levels, unsustainable earnings growth, negative free cash flow for AI companies by 2027, and concentrated market gains in fewer stocks. Rising Treasury yields above 5% could further destabilize AI funding and equities.