Almost a month ago, information appeared on the Internet that YouTube began testing a new policy regarding the quality of 4K recordings. After implementing the changes for some of the accounts, users received access to 4K quality, which includes video resolution 3840x2160px, only after purchasing an additional Premium subscription. This was evidenced by the "Premium" note next to the 2160p resolution variant. YouTube, however, responded on social media by reassuring its users.
YouTube calls the changes to the 4K availability available as an experiment. After several days of testing, YouTube finally restored all users access to 4K quality on the portal, regardless of whether they have purchased a YouTube Premium subscription or not. In the near future, the availability of 4K for all users should not change, but YouTube is avoiding comments regarding results of the experiment.