There are 2 repositories under youtubei topic.
A wrapper around YouTube's internal API — reverse engineering InnerTube
The ultimate dirty API Client for the internal YouTube API (Innertube API) with a big and growing coverage of actions and endpoints
2005 YouTube frontend that uses youtubei
A frontend for the InnerTube/YouTubeI API, designed after YouTube's 2013 Hitchhiker.
V3 is the alternative solution to a fast and responsive YouTube frontend which combines performance with beauty, bringing back Google's best web layout.
API reference for YouTube's internal API, InnerTube.