Microsoft has lost an AI expert and OpenAI gained one, after the former’s VP of generative AI research Sebastian Bubeck left for the latter. The Information first reported the move, and Reuters also confirmed the departure with Microsoft.

We know Bubeck as one of the main authors of papers describing Microsoft’s Phi models, a series of extra-small language and vision models intended to help push AI applications to edge devices. That kind of expertise is increasingly important as large, centralized models like OpenAI’s GPT-4o give way in some markets to on-device models that work quickly, privately, and offline.

While Bubeck’s new role at OpenAI is still a mystery, it seems likely he’ll be working on the efficiency and small-model side of things — a corner of the AI world where OpenAI is currently less prominent.