Twitter has informed its business partners that "Twitter, Inc. has changed its name to X Corp." and told them to use the latter name in all official dealings, according to an email sent to its partners. The email ends with "X Corp. (formerly Twitter, Inc.)," highlighting the change. Twitter's terms of service now lists "X Corp." as the company's official name, but it's unclear when this change was made.
Additionally, Twitter will retain the name of the social media site. (Forbes)