Late last year, a trio of engineers who had just helped Apple modernize its search technology began working on the type of technology underlying ChatGPT, the chatbot from OpenAI that has captivated the public since it launched last November. For Apple, there was only one problem: The engineers no longer worked there. They had left the company to work on the technology, known as large-language models, at Google.

The three men—Srinivasan Venkatachary, Steven Baker and Anand Shukla—left Apple last fall in part because they believed Google was a better place to work on LLMs, which are capable of understanding language and generating humanlike responses, according to two people familiar with their thinking. They are a hot commodity: Google wanted them badly enough that its CEO, Sundar Pichai, personally wooed the group, while Apple CEO Tim Cook tried to persuade them to stay, according to two people who spoke to Venkatachary about it. They’re now working on Google’s efforts to reduce the cost of training and improving the accuracy of LLMs and the products based on these models, according to one of those people.