The straightforward answer is No, there's a catch, however. It is allowed to stream on both Twitch and YouTube (or any other site) simultaneously, provided you aren't an affiliate of Twitch or a Twitch partner. However, embedding the live stream on another site is allowed.  For affiliates and Twitch partners, there's an exclusivity rule which says live content or pre-recorded streamed contents are to remain on Twitch for 24 hours before they can be broadcasted or posted to another site or platform.  In other words, if you are a Twitch affiliate or Twitch partner, you are not allowed to live stream on both Twitch and YouTube at the same time. Even if the video was pre-recorded and streamed on Twitch, they'll consider the video as a Live Stream, and you aren't also allowed to share this.  Most people do stream on multiple platforms but keep the YouTube stream private, then when the 24 hours elapse, they make it public.  Their exclusivity rule doesn't stop you from streaming brand new content on YouTube or any other platform AFTER you've ended your Twitch unique stream. You can find more details here.