Per Axios, SEC, and Business Insider
Jack Dorsey, the co-founder of Twitter, retained a 2.4% stake in Twitter after Elon Musk's $44 billion acquisition.
Per an SEC filing, Dorsey retained his 18,042,428 shares which would total $1 billion, by rolling it over into a stake.
The co-founder rolled over his Twitter shares on October 27, when the acquisition was finalized, to the new holding company for Twitter, X Holdings I Inc.