The Lightstream Integration currently is in beta and restricted to Mixer partners and Pro subscribers at this time. If you can’t wait to get started, you can gain instant access by subscribing to Mixer Pro. Find out more about Mixer Pro here.
At the moment, there's no ETA on when the Mixer Integration will be released outside of Mixer Pro. The integration is predicted to remain in beta for a while longer and we're working closely with Mixer to figure out the best game plan that works for our users.