New Delhi, Feb. 24 -- Artificial intelligence is advancing at startling speed. The latest models can now complete complex, hours-long tasks with little human supervision. This month one of OpenAI's models helped derive a new result in theoretical physics. No wonder an essay declaring that "Something Big is Happening" has gone viral.

Is something big happening to the economy, too? Scott Bessent, America's treasury secretary, predicted last year that AI would soon start "biting"-meaning that it would lead to noticeable improvements in productivity. Kevin Warsh, President Donald Trump's nominee to lead the Federal Reserve, is counting on an AI-driven productivity boom to help tame inflation.

A puzzle in America's macroeconomic data appears...