Facebook parent Meta has lost some of its top artificial intelligence scientists this year as the company continues its pivot toward the metaverse.

At least four prominent members of Meta AI have departed in recent months, according to people familiar with the matter and LinkedIn analysis. Between them, the scientists have published dozens of academic papers in world-renowned journals and made multiple breakthroughs that Meta has used to enhance Facebook and Instagram.

Karl Hermann, an AI entrepreneur who used to work at rival lab DeepMind, told CNBC on Monday the true figure could be more like half a dozen, adding that the company’s London AI lab had seen an alarming number of exits. “Meta’s London office just collapsed and they lost most of their [top] researchers in the span of six weeks,” he said.

Neil Lawrence, professor of machine learning at the University of Cambridge, told CNBC that he wasn’t surprised. “Mark’s [Zuckerberg] gone all Meta now … and they never invested properly in anything in London in the first place,” he said.

Those who have left the company include Edward Grefenstette, a research scientist that led Meta’s efforts on a branch of AI known as reinforcement learning, who departed in February. He declined to comment when contacted by CNBC.

Heinrich Kuttler, one of Meta AI’s research engineering managers, left in recent weeks to join Inflection AI, a start-up set up by DeepMind co-founder Mustafa Suleyman and LinkedIn billionaire Reid Hoffman. Kuttler joined Meta in Jan. 2019 after spending over two years at DeepMind.

Another recent departure is Ahmad Beirami who left his research scientist position at Meta in January and joined Google in the same role.

And last year, in December, Douwe Kiela left his research scientist role at Meta after spending five years at the company. He’s now head of research at AI start-up Hugging Face.

Kuttler, Beirami and Kiela did not immediately respond to a CNBC request for comment.

A number of other Meta AI staff have either left or are expected to leave in the coming weeks, a person familiar with the matter told CNBC, asking to remain anonymous due to the sensitive nature of the issue. They added that there’s no one reason why people were leaving.

“Some people jump to another big lab because they feel it will advance their career or research agenda better,” the source said.

“Others go because comp or hiring potential for their team is better elsewhere,” the source added. “Others just want to do a start-up or get involved with a smaller company. For some it might be tied to Meta stock tanking, but I wouldn’t say that’s necessarily the main reason.”

Meta’s Chief AI Scientist Yann LeCun, who co-founded the firm’s AI lab in 2013 after a dinner at Zuckerberg’s house, told CNBC via email that “people have changing interest[s] and move on.”

He added: “Ed [Grefenstette] is joining an unnamed start-up. I’m sad he has left. But I understand that people’s interests shift. I’m not sure what Heinrich’s plans are. There is no underlying common cause that I know about. There has been no detectable migration from FAIR (Facebook AI Research) London nor from the other sites.”

It’s worth noting that several people from DeepMind and other AI labs have also joined Meta over the last couple of years.

Fueled by the belief that AI is going to change the world, U.S. tech giants have been investing heavily in the area over the last few years with most of the money going toward hiring top talent from leading colleges like Oxford and Cambridge in the U.K., and MIT, Stanford and NYU in the U.S.

The latest departures at Meta AI come on the heels of several other big exits over the last two years. Rob Fergus, the co-founder of Meta’s AI lab, left Meta in 2020 to join DeepMind and build up a DeepMind team in New York.

Elsewhere, Marc’Aurelio Ranzato left his research scientist manager role at Meta AI last August and joined DeepMind.

Beyond Meta’s AI lab, there were a number of other major exits across the company in 2021.