The social media network's website showed the company's new logo, but its URL was still showing as twitter.com and the blue "Tweet" button was visible, suggesting the rebrand was not yet finalized.
Musk and the company's new chief executive Linda Yaccarino announced the rebranding Sunday, saying the company would be renamed X and move later into payments, banking, and commerce.
Founded in 2006, Twitter takes its name from the sound of birds chattering, and it has used avian branding since its early days, when the company bought a stock symbol of a light blue bird for $15, according to the design website Creative Bloq.
Musk changed his profile picture late Sunday to the company's new logo, which he described as "minimalist art deco," and updated his Twitter bio to "X.com," which now redirects to twitter.com.
He also tweeted that under the site's new identity, a post would be called "an X."
Musk had already named Twitter's parent company the X Corporation and has said his takeover of the social media giant was "an accelerant to creating X, the everything app" -- a reference to the X.com company he founded in 1999, a later version of which went on to become online payments giant PayPal.
Such an app could still function as a social media platform and also include messaging and mobile payments.
Musk had previously said he wanted to create a super-app modeled on China's WeChat, a social media platform that also offers messaging and mobile payments.
"You basically live on WeChat in China because it's so usable and helpful to daily life, and I think if we can achieve that, or even get close to that at Twitter, it would be an immense success," he told a company town hall meeting in June last year.
The new logo was projected onto the facade of Twitter's San Francisco headquarters on Sunday night.
"Powered by AI, X will connect us in ways we're just beginning to imagine," Yaccarino tweeted earlier.
Yaccarino, a former advertising sales executive at NBCUniversal who Musk hired last month to be Twitter's CEO, said the social media platform was on the cusp of broadening its scope.
"X is the future state of unlimited interactivity - centered in audio, video, messaging, payments/banking - creating a global marketplace for ideas, goods, services, and opportunities."
Simon Kemp, CEO of digital consultancy Kepios, said he was skeptical that Twitter could evolve into a super-app.
"Given how Musk has treated Twitter's own employees since the acquisition, I don't imagine many developers will rush to build third-party apps to integrate into the Twitter ecosystem unless Musk can offer outstanding incentives, and that'll be extra tricky given the company's existing debt."
But he also said the platform had the potential to become "a great (global and paid) news aggregator."
- New revenue streams -
Since Musk bought Twitter for $44 billion last October, the platform's advertising business has partially collapsed as marketers soured on Musk's management style and mass firings at the company that gutted content moderation.
In response, the billionaire SpaceX boss has moved toward introducing payments and commerce through the platform in a search for new revenue.
Twitter is thought to have around 200 million daily active users, but it has suffered repeated technical failures since Musk sacked much of its staff.
Many users and advertisers alike have responded adversely to the social media site's new charges for previously free services, its changes to content moderation, and the return of previously banned right-wing accounts.
Musk said this month that Twitter had lost roughly half of its advertising revenue since he took control.
Facebook parent Meta also launched its text-based platform this month, called Threads, which has up to 150 million users according to some estimates.
But the amount of time users spend on the rival app has plummeted in the weeks since its launch, according to data from market analysis firm Sensor Tower.