Artificial downtime: UK evidence on investor GenAI reliance and trading behaviour from ChatGPT and Claude outages

Sammanfattning

In this paper, we provide updated evidence on the extent to which investors rely on generative artificial intelligence (GenAI) tools, and what disruptions to these tools reveal about their role in financial markets. We exploit unanticipated outages to ChatGPT and Claude, between March 2025 and February 2026, as plausibly exogenous shocks to investors' access to GenAI tools, and measure changes in trading volume on the London Stock Exchange. We document a significant decline in trading activity during GenAI outage periods. The effect differs systematically across platforms and is primarily driven by Claude outages, with ChatGPT outages producing no statistically significant effect across any specification. We further find suggestive, though not conclusive, evidence that the outage effect is materially stronger on accounting disclosure days than on other regulatory and non-regulatory news days. Finally, a dynamic analysis illustrates that trading activity declines immediately following outages, with the effect intensifying before partially reversing. Taken together, our findings suggest that investors rely on GenAI tools in economically meaningful ways, such that disruptions to a single platform produce observable effects on market activity, even in a more mature multi-tool environment.