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, AI-related developments have been a key driver of earnings revisions, and those upward revisions have in turn been a crucial factor behind stock gains this year. The warning is that if the pace of AI model development slows, that support could weaken.

The mechanism matters more than the headline. Earnings revisions — analysts raising their profit estimates — tend to feed directly into valuations, so a slowdown in AI progress would not need to hurt current results to affect prices. It could simply stall the forward estimates that investors have been paying up for.

What to watch: the cadence of major model releases and capability updates, and whether analysts begin trimming AI-linked earnings forecasts. Neither is a prediction of a decline, but both are worth monitoring as a gauge of whether the market's most crowded theme still has fundamental momentum behind it.