A.I. chatbots are fun, sometimes even useful and, until recently, endowed with the uncanny ability to mesmerize investors and fuel the U.S. stock market.

But the excellent performance of a new, relatively cheap artificial intelligence engine from a Chinese start-up, DeepSeek, has perturbed the market and complicated the A.I. story.

Investors are re-evaluating prominent companies swept up in A.I. fever, including Nvidia, Meta, Alphabet, Microsoft, Amazon, Tesla and the private start-up OpenAI. The notion that full-blown superhuman intelligence is imminent has spurred the-sky-is-the-limit valuations, as well as concerns about the political and social risks posed by advanced intelligence.

One immediate question: Is the main approach to developing A.I. in the United States — pouring billions of dollars into chips and infrastructure — worth the expenditure for all companies if similar results can be achieved far more cheaply? DeepSeek’s lower-cost innovations add urgency to bigger, longstanding financial questions: How much are artificial intelligence companies really worth, and what will the broader economic value of A.I. ultimately be?

Daron Acemoglu, a winner of the 2024 Nobel in economic science, gave me some answers. “There is a lot of hype in the industry,” he told me in a telephone conversation. Yes, he said, A.I. companies have made some “impressive achievements,” but he added that many financial and economic calculations were being based on mere “projections into the future that are sometimes exaggerated.”

Professor Acemoglu, an M.I.T. economist with an interest in the impact of technical innovations on global economics, is skeptical about the more fervent A.I. claims. He ranks A.I. as a significant advance, perhaps with a macroeconomic effect akin to the telephone, which was no small thing.