https://www.cnet.com/news/twitch-launches-its-first-game-karaoke-fest-twitch-sings/

Twitch Sings has been available for some streamers to play in a pilot beta version for about six months, and broadcasts of those performances have been available for anyone to watch. Saturday marks Twitch opening up the game for almost anyone to play. 

The company called it a worldwide launch, but a few markets are excluded because of issues around licensing rights. South Korea, for example, isn't included.