Twitter shares jumped more than 26% premarket after a 13G filing revealed Elon Musk has taken a passive stake in the social media company. 

According to the 13G filing, Musk has accumulated 73,486,938 shares of Twitter, representing a 9.2% (based on 800,641,166 shares of Common Stock outstanding). The stake is worth nearly $2.9 billion, based on Friday's closing price.