Twitter shares are up 12% in premarket trading. The deal would value the company at about $43B and is what Musk says is his "best and final offer."
"Twitter has extraordinary potential. I will unlock it," Musk said in an amended 13-D filing.
He is the company's largest shareholder and said he would reconsider his holdings if his bid is rejected.
Musk was expected to join the board of Twitter after disclosing a 9% stake in the company, but then turned down the offer, leading to speculation he could go hostile.
The offer represents an 18% premium over Twitter's closing price yesterday. Musk says it is a 54% premium over the day before he began investing in the social media company.
"I invested in Twitter as I believe in its potential to be the platform for free speech around the globe, and I believe free speech is a societal imperative for a functioning democracy," Musk said. "However, since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form. Twitter needs to be transformed as a private company."
The number $54.20 is significant as Musk likes to make reference to "420" - well known in cannabis culture as the supposed best time to get high. His infamous tweet to take Tesla private (which ran him afoul with the SEC) was for $420 per share.
Digital World Acquisition (DWAC), the SPAC that's home to Donald Trump's Truth Social, is down 4% premarket.
Read the full filing.