AI has been carrying the stock market. An industry pause could pull the rug out, warns this Wall Street giant.

Citigroup is flagging a concentration risk that has quietly underpinned this year's equity gains: the artificial-intelligence trade. According to the bank, if the pace of AI model development slows, analysts may begin revising earnings estimates lower — and those upward revisions have been a key driver of stock performance in 2024.

The logic matters for investors because it highlights how much of the market's advance rests on expectations rather than realized results. AI-related names have commanded premium valuations on the assumption that model capabilities, and the revenue they generate, will keep expanding. A pause in that cadence would test those assumptions directly.

What to watch: whether upcoming model releases and corporate AI spending plans sustain the current trajectory, and how quickly earnings estimates react if they don't. For now, the warning is a reminder that narrow leadership can cut both ways — the same theme powering gains could amplify any disappointment.