June 23, 2026 – Alphabet shares plummeted Monday in the most dramatic single-day selloff the company has seen in nearly a year, wiping out roughly $210 billion in market value after two of its most celebrated AI architects defected to rival labs within just 72 hours.
The stock touched an intraday low of 340.94—downmorethan7348.78, a 5.08% decline that erased weeks of prior gains.
The catalyst was a startling brain drain at DeepMind. On Wednesday, June 18, Noam Shazeer, a co-author of the landmark Transformer paper and the architect behind Google’s MoE (Mixture-of-Experts) strategy, announced he was leaving for OpenAI. Shazeer, who had returned to Google less than two years ago as part of the $2.7 billion Character.AI acquisition, held the title of VP of Engineering and co-lead of the Gemini model.
Two days later, on June 20, John Jumper — the driving force behind AlphaFold and a 2024 Nobel laureate in Chemistry alongside DeepMind CEO Demis Hassabis — confirmed his own departure for Anthropic. Jumper, a DeepMind Engineering Fellow, is widely regarded as the leading figure in computational biology.
With those exits, all eight original authors of the Transformer paper have now left Google, and AlphaFold, once the crown jewel of the company’s AI portfolio, is without its principal steward.
Compounding the damage, Alphabet’s stake in SpaceX shed significant value as SpaceX shares dropped over 9% on the same day. Growing investor skepticism about the return on massive AI capital expenditures across Big Tech further accelerated the rout.
