Shares of Alphabet dropped Monday in the first trading session since John Jumper, a senior research scientist and Nobel Prize winner, said he was leaving Google DeepMind for artificial-intelligence start-up Anthropic.

Alphabet stock fell 5% to $349.56, its largest daily percentage decline in more than a year. Shares have fallen 8.1% this month but remain up about 11.7% this year.

The Google parent lost $225 billion in market value on Monday, the largest single-day market capitalization loss for Alphabet ever, according to Dow Jones Market Data.

On Friday, in a post on X, Jumper said he was leaving Google DeepMind after nine years for Anthropic. DeepMind is the backbone of Google’s advanced AI models.

Alphabet confirmed Jumper’s departure.

“We are grateful for John’s significant contributions to Google DeepMind’s work in advancing science and AI,” according to a statement to Barron’s. “We wish him well in his next chapter.”

Anthropic separately confirmed to Barron’s that Jumper will be joining the company. The AI start-up declined to comment on how it is prioritizing talent acquisition or whether Anthropic plans to make any more high-level hires in the near future.

Jumper helped create AlphaFold, DeepMind’s AI system that predicts protein structures from their amino acid sequences.

His departure comes shortly after Noam Shazeer, a vice president of engineering at Google and a key member of the Google Gemini team, said he was leaving for OpenAI, the start-up that created ChatGPT.

“Losing John is a big loss for Google and there is no way to sugarcoat it,” Wedbush Securities analyst Dan Ives told Barron’s. Ives added that Anthropic “got a special one” in Jumper and that he has been integral in pushing forward the AI boom. “Investors do not want to see this and the negative knee jerk reaction is being seen,” Ives said of Alphabet stock’s drop.

Big Tech along with AI start-ups Anthropic and OpenAI are currently fighting for the top AI talent in the marketplace as they all vie for superiority in the space. As a result, pay packages have stretched into the hundreds of millions, and big-money acquisitions of smaller rivals have become commonplace.

Both Anthropic and OpenAI earlier this month announced plans to go public as competition is now not only for talent but for investor dollars.

“The departures of Noam Shazeer to OpenAI and John Jumper to Anthropic within a couple of days are raising the concern that Google is losing the war for talent at the frontier of AI,” D.A. Davidson analyst Gil Luria told Barron’s in an email.

“Google had the state-of-the-art model for a few weeks last year which helped it get credit as an AI winner but has fallen off since, and these departures may mean it is falling behind,” Luria added.