Elon Musk took a 9.2% stake in Twitter Inc. to become the platform’s biggest shareholder, a week after hinting he might shake up the social media industry.

– Tesla CEO has regularly questioned Silicon Valley giant – Shares in platform jump as much as 26%, the most since 2018

Twitter shares surged as much as 26% after Musk’s purchase was revealed Monday in a regulatory filing, the stock’s biggest intraday increase in more than four years.

the stock’s biggest intraday increase in more than four years. The stake is worth about $2.89 billion, based on Friday’s market close.

Musk, 50, polled his more than 80 million followers on Twitter last month, asking them whether the company adheres to the principles of free speech.

After more than 70% said no, he asked whether a new platform was needed and said he was giving serious thought to starting his own.

Musk has been one of the biggest personalities on Twitter and has regularly run into trouble on the platform. The Tesla Inc.

chief executive officer is currently seeking to exit a 2018 deal with the U.S. Securities and Exchange Commission that put controls in place related to his tweeting about the electric-car maker.

The announcement will be yet another major test for new Twitter CEO Parag Agrawal, who replaced Jack Dorsey after he unexpectedly resigned in November.

Musk has lambasted Twitter’s recent development of profile pictures linked to non-fungible tokens, saying the social media company has the wrong priorities.