The spat began days earlier, on May 27, after Musk took to X to encourage people to apply for roles at his AI startup, xAI. The company, which last week announced it had raised $6 billion, is in a battle for AI engineers with high-profile startups, such as OpenAI and Anthropic, as well as top tech companies, including Google, Microsoft, Amazon and Meta.

Meta is trying to differentiate itself in the world of large language models, or LLMs, which have powered the recent boom in generative AI product development. While LLMs from xAI, OpenAI and Google are closed and proprietary for now, Meta is touting its Llama family of models as open source, meaning other researchers can copy, tweak or otherwise use them for their own AI initiatives.

In response to Musk’s promotional post, LeCun wrote, “Join xAI if you can stand a boss who makes promises that can’t be met, claims AI will ‘kill everyone’ and spews wild ‘conspiracy theories on his own social platform.'”

They continued going at it on Monday after Dr. Anthony Fauci testified publicly for the first time since leaving the government in 2022. Fauci appeared before the House Select Subcommittee on the Coronavirus Pandemic, facing broad criticism from Republicans who have long claimed he lied about the genesis of Covid-19.

Musk, who has previously called for the prosecution of Fauci, posted on X, “Why do Dems love Fauci so much.” He also unfollowed LeCun.

In response to being unfollowed, LeCun wrote, “Must have been my tweet in defense of Anthony Fauci.”

He followed by writing, “Elon’s call for Fauci to be prosecuted and imprisoned is pretty high up on the scale of anti-science a–holery.”

While Musk and Meta CEO Mark Zuckerberg have engaged in a yearslong public dispute and were even goading each other for months last year about a possible cage match, few tech leaders have been willing to criticize Musk in the open or bet against his companies.

Microsoft co-founder Bill Gates previously shorted Tesla stock. Investor Mark Cuban criticized Musk over his opposition to corporate Diversity, Equity, and Inclusion (DEI) efforts. And Meta co-founder Dustin Moskovitz has accused Tesla of consumer fraud.

In posts on X and LinkedIn over the weekend, LeCun said he disagrees with Musk’s secrecy when it comes to developing new technology and products and the “blatantly false” predictions he shares with the public, in addition to how he chooses to share “dangerous political opinions” and conspiracy theories.

Musk said in a post on X Monday that LeCun has been “out of touch with AI for a long time.” A Google Scholar link shared by LeCun indicates he has published 80 technical papers since January 2022.

LeCun and Musk didn’t respond to requests for comment on Monday.

The “blatantly false” predictions LeCun referenced included Musk’s claims that artificial general intelligence would arrive next year and that Tesla would bring 1 million robotaxis to market by 2020.

The latter promise came on a call with investors in 2019. At the time, Musk said robotaxis would make Tesla a company worth $500 billion. Tesla’s market cap topped $1 trillion in 2021, but the company still hasn’t delivered a single robotaxi.

Musk has also shared lofty goals for his brain implant startup Neuralink. He’s claimed Neuralink’s devices could enable “superhuman cognition” and “solve” autism and schizophrenia. During a “show and tell” recruitment event in late 2022, Musk said he plans to get an implant himself.

The company has implanted its flagship system in one human patient so far and has not received FDA approval for its technology.

LeCun was also critical of how Musk takes credit for the work of others. He pointed out that Musk’s only technical publication on Google Scholar is related to Neuralink. It was published in the Journal of Medical Internet Research in 2019. Musk is listed as the lead author, while the blanket term “Neuralink” is listed as the second author.

“I’m sure the scientists who hide behind this collective name are super happy about that,” LeCun said on X. “I just hope they won’t die bitter and forgotten.”

WATCH: Musk and Trump to team up?