Elon Musk buys 9.2% stake in Twitter, making it the largest shareholder

News of the purchase sent shares of Twitter †TWTR† rising 20% in pre-market trading. Musk has not disclosed what he paid for the stock, but his stake was worth $2.9 billion as of the close of trading Friday and $3.5 billion after its peak early Monday.

Musk’s filing did not disclose the purpose of the purchase or plans for the company. But he has been a high-profile critic of Twitter policy in the past. Last month, he said he was “thinking seriously” about creating a new social media platform.

“Since Twitter acts as the de facto public town square, failure to adhere to the principles of free speech fundamentally undermines democracy,” Musk said. tweeted last month. “What must be done?”

Any time an investor buys 5% or more of a company’s stock, they must disclose the purchase in filings with the Securities and Exchange Commission. While a stake of less than 10% in a company is considered “passive” in Wall Street’s eyes, it could indicate an attempt by Musk to take a more active role in how Twitter is run. That’s one of the factors driving other investors to buy stocks and push the price up early Monday.

“I think he plans to get active and force change at Twitter,” said Dan Ives, technical analyst at Wedbush Securities. “This is a shot across the board for Twitter’s board and management team to spark discussions.”

But Ives said it probably isn’t realistic for Musk or anyone else to start from scratch building a new, competitive platform. So it makes more sense for him to try and change the practices on Twitter itself.

Musk has 80 million Twitter followers, far more than any CEO.