FINGERS CROSSED: ‘We’re not in a bubble yet’ because only 3 out of 4 conditions are met, top economist says. Cue the OpenAI IPO.

Owen Lamont, a portfolio manager at Acadian Asset Management and a former University of Chicago finance professor, said that while the market looks and feels frothy, we are not currently in an AI bubble. As he talked to Fortune from his office in Boston, the S&P 500 breached 7,000 for the first time, but he wasn’t dissuaded. To Lamont, the tell-tale sign of a bubble is equity issuance, when corporate executives, the ultimate insiders, rush to sell overvalued stock to the public.

“Part of the reason I think there’s not a bubble is I don’t see the smart money as acting like there’s a bubble,” he told Fortune. “Maybe I should say there’s not a bubble yet.”

In his view, the smoking gun for a bubble forming would be companies going public and selling equity. That would be a play for the dumb money, he added.
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Lamont’s bubble-detection framework relies on “Four Horsemen”: overvaluation, bubble beliefs, issuance, and inflows. While he conceded that three of these are present in the market of early 2026—valuations are high, retail investors are piling in, and sentiment is frothy—the absence of issuance disqualifies the current cycle from bubble status.

In the meantime, enjoy the ride.