Teresios Bundi moved from a farming village to Nairobi in 2011 to attend university. A friend suggested writing essays for overseas college students. His first assignment paid $7 for three hours of work. Over 12 years, Mr. Bundi estimates he wrote more than 2,500 essays, sometimes three daily, while completing his public health degree.

At its peak early this decade, researchers estimated at least 40,000 people in Nairobi were paid to do others' homework. Mr. Bundi built an essay-writing business charging $40 to $70 per paper, hiring students and renting a house near a university with desks and fast internet.

In 2022, OpenAI released ChatGPT. Students worldwide calculated: why pay a Kenyan freelancer when AI could do it? Essay work thinned, rates fell, and the industry shrank to almost nothing. Mr. Bundi closed his business and now works for a German government development organization helping young Kenyans.

Mark Graham, an Oxford University professor studying the global gig economy, said: "A.I. has come in and taken big chunks of these labor markets." Similar declines hit Kenyans transcribing meetings through Upwork and Fiverr and flagging Facebook posts.