Mr. Musk has said that buying Twitter is “an accelerant to creating X,” and the corporate entity he created to purchase and control Twitter is called X Holdings.

Mr. Musk spoke on a Twitter audio livestream early Sunday to say he was changing Twitter’s logo. “It should have been done a long time ago,” he said. “Sorry it took so long.”

A few hours later, Mr. Musk said in an email to Twitter’s employees that “we are indeed changing to X” and that it was happening “today.” “This is my last message from a Twitter email,” he wrote, before signing off with a salute emoji.

Mr. Musk has few barriers to making such alterations at the company after taking it private as part of his acquisition of the firm. But he could still encounter resistance from the banks that have lent him billions of dollars and the private investors he brought into the deal, who could raise concerns about jettisoning one of Twitter’s most visible assets.

The company saw its advertising revenue plummet amid the departure of sales executives and worries that the site had become more prone to problematic content. It now faces a well-funded rival in Threads, the recently introduced Twitter-like service from Meta, the owner of Facebook.