Silicon Valley’s tech bros are having a difficult few weeks. A growing number of investors worry that artificial intelligence (AI) will not deliver the vast profits they seek. Since peaking last month the share prices of Western firms driving the ai revolution have dropped by 15%. A growing number of observers now question the limitations of large language models, which power services such as ChatGPT. Big tech firms have spent tens of billions of dollars on ai models, with even more extravagant promises of future outlays. Yet according to the latest data from the Census Bureau, only 4.8% of American companies use ai to produce goods and services, down from a high of 5.4% early this year. Roughly the same share intend to do so within the next year.