Reddit user Dean Cobb revealed on Monday night that a new dark mode was already live as an option in the Settings section of the app after updating to version 13.01.4.
However, as of this morning, rollout of the feature still seems to be limited to a handful of users, suggesting a selective server-side activation on YouTube's end.
App Store release notes for YouTube version 13.0.1 make no mention of the dark mode addition either, but we'll update this article if the rollout gains pace anytime soon.
YouTube is a free download for iPhone and iPad. [Direct Link]