Adult content and nudity has been present on Twitter for years and -- unlike Facebook or Instagram -- was never explicitly banned even before Musk's takeover in late 2022.

The new guidelines, first reported by Tech Crunch on Monday, explicitly permit users to share adult content "as long as it is consensually produced and distributed adult nudity or sexual behavior."

X updated the guidelines over the weekend, stating that "sexual expression, visual or written, can be a legitimate form of artistic expression."

Under the new policy, posting adult content is formally within the rules as long as it is labeled and not prominently displayed, such as in profile pictures or account banners.

Accounts that regularly post adult content will be required to automatically mark their image and video posts as sensitive content.

Adult content will also be prohibited for users identified as children or adult users who choose not to view it.

The policy extends to AI-generated content, animations, cartoons, hentai and anime.

X's safety team tweeted the new guidelines would "bring more clarity to our rules and transparency into enforcement of these areas."

Since acquiring Twitter in 2022 with the stated intention of promoting free speech, Musk has faced criticism for slashing content moderation teams.

Under his ownership, the platform has also experienced technical issues and reinstated accounts of right-wing conspiracy theorists and former US President Donald Trump.

Musk also aims to expand X's revenue base beyond advertising and transform it into a "super app" similar to China's WeChat, which integrates messaging, voice and video calling, social media, mobile payments and online booking services.