Alphabet shares closed down roughly 5% on Monday, the company’s steepest single-day slide since a 7% drop in May 2025, after a week in which Google DeepMind lost five high-profile researchers to its two largest rivals. Intraday, the stock was off 7.2%, the worst move since February. The market, which had spent a year insisting that Google’s vertical integration would eventually pay off, decided in a single session that it wouldn’t.

The names matter. Noam Shazeer, vice president of engineering and co-lead of the Gemini models, announced last Wednesday he was leaving for OpenAI. Google had effectively acqui-hired Character.AI for $2.7 billion in part to bring him back. Over the weekend, John Jumper, who shared the 2024 Nobel Prize in Chemistry with DeepMind CEO Demis Hassabis for AlphaFold’s prediction of 3D protein structures from amino acid sequences, said he was going to Anthropic. Bloomberg then reported Tuesday that Jonas Adler and Alexander Pritzel, both key players on Gemini, were poised to follow Jumper to Anthropic.

Five in a week.

The proximate cause is legible enough. Gemini 3.5 Flash and Gemini 3.1 Pro have been ranking outside the top five on benchmark leaderboards, trailing Anthropic, OpenAI, and Chinese labs like Zhipu AI and MiniMax. Anthropic has shipped two significant Claude Opus updates and unveiled Mythos, a new model class that’s said to lead in long-range autonomous tasks, particularly coding and cyber. Bloomberg reported that just before Shazeer’s announcement, compute dedicated to one of his projects had been reassigned to a London-based DeepMind team. The signal there’s unmistakable to anyone who’s worked inside a research org.

Fortune’s read on Jumper was that he doesn’t strike observers as someone primarily motivated by money. That’s the part that should worry Alphabet most. A Nobel laureate doesn’t leave the lab that built AlphaFold for a comp package. He leaves because he thinks the work is better elsewhere.

Both Anthropic and OpenAI are on the cusp of going public. Equity granted now prices into an IPO window measured in quarters, not years, and the researchers leaving Mountain View understand the math precisely. Monday’s tape suggests the buy side has started doing the same arithmetic, only in reverse.

Sources