Key takeaways: 

• Musk owns 73,486,938 shares of Twitter, which denotes a 9.2% passive stake in the firm, according to the Securities and Exchange Commission 13G filing released Monday.
• Based on Twitter's closing cost Friday, the stake is valued at $2.89 billion.
• The Musk purchase comes less than two weeks after Musk slammed the firm, polling people on Twitter regarding whether Twitter sticks to free speech principles.

Outspoken Tesla CEO Elon Musk bought a significant stake in Twitter, making him the largest outside shareholder in the social media stock. Not long after blaming the firm for what he said was its loss to uphold the tenets of free speech.

Musk holds 73,486,938 shares of Twitter, which means a 9.2% passive stake in the firm, according to a Securities and Exchange Commission 13G filing released Monday. Based on Twitter's closing price Friday, the stake is valued at $2.89 billion.

The purchase comes less than two weeks after Musk criticized the firm, polling people on Twitter regarding whether it adheres to free speech tenets. "Given that Twitter serves as the de facto public town square, failing to adhere to free speech principles fundamentally damages democracy," Musk tweeted. "What should be done?"

Musk also said he was considering making a new social media platform the previous month.

While it is categorized as a passive stake, investors were bidding shares higher on the case this could lead to something more. The Twitter stock flooded more than 29% in the afternoon.

"Musk could attempt to take a more assertive pose here on Twitter," Wedbush analyst Dan Ives said Monday on CNBC's "Squawk Box." "This ultimately could lead to some kind of buyout."

"This makes sense given what Musk has been talking about, at least from a social media view," Ives said.