Alphabet shares fell 4 per cent on Wednesday after the company announced a sweeping leadership shake-up at its artificial intelligence division, fueling investor concerns over delays to its flagship Gemini AI model and competitive pressure from rivals OpenAI and Anthropic. The restructuring marks one of the biggest management changes at Google DeepMind since the company merged its AI research teams in 2023, with the latest version of Gemini still unreleased despite an earlier target of launching in June. Nobel Prize-winning AI researcher Demis Hassabis will step down as chief executive of Google DeepMind to become Alphabet's newly created chief scientist, focusing on artificial general intelligence. Alphabet CEO Sundar Pichai said the move had been under discussion for some time. Koray Kavukcuoglu, currently DeepMind's chief technology officer and Alphabet's chief AI architect, will take over day-to-day leadership as senior vice president. The overhaul coincided with the departure of several researchers, including veteran engineer Jeff Dean, Sanjay Ghemawat, Oriol Vinyals and Quoc Le, who left to launch a startup called Discovery Loop focusing on machine learning, scientific research and engineering, operating as a public benefit corporation. Alphabet did not explain the timing of the departures. Earlier this summer, senior researcher Noam Shazeer departed for OpenAI, while Nobel laureate John Jumper announced he would join Anthropic. Gemini 3, released last November, was widely viewed as narrowing the technology gap.