Claire Aubin, a historian who specializes in Nazism within the United States, agreed Musk's gesture was a "sieg heil," or Nazi salute.

"My professional opinion is that you're all right, you should believe your eyes," Aubin posted on X, aligning with those who found the gesture was an overt reference to Nazis.

Ruth Ben-Ghiat, a historian of fascism, also found the gesture "was a Nazi salute -- and a very belligerent one too," she said on X.

At this point, Musk put his right hand on his chest before extending it straight out with his palm facing down and his fingers touching, a gesture widely recognized as the “Roman salute.” Adopted by the fascist movement a century ago, it was most famously used by Adolf Hitler and the Nazi Party in Germany, and is to this day associated with the fascist right, especially in Italy.

“The entire neo-Nazi movement seems to be eating it up,” says Nick Martin, an investigative journalist who closely tracks extremist groups and runs the online publication The Informant. “He gave two unmistakable Nazi salutes and they got the message loud and clear.”

“WE ARE FUCKING BACK” the administrator of a Nazi meme channel on Telegram wrote under a clip of Musk giving the salute. Members of the group responded with the lightning bolt emoji, a well-known neo-Nazi reference to the SS.

Evan Kilgore, a right-wing political commentator, wrote on X: “Holy crap … did Elon Musk just Heil Hitler at the Trump Inauguration Rally in Washington DC… This is incredible.” Kilgore later wrote: “We are so back.”

Musk also retweeted videos of his speech on his X handle and said, "The future is so exciting." The video which he retweeted, however, did not feature the hand gestures.

Musk has a history of making Nazi jokes on social media, and back in September, the X CEO promoted former Fox News host Tucker Carlson’s widely condemned interview with a Nazi apologist (but he later deleted the post, in a rare move for the billionaire).