
Spotify allows instant listening to specific tracks or albums with virtually no buffering delay. It was launched in the fall of 2008 and had approximately 10 million users by September 2010.
Encouragement Designs and Instrumental Variables for A/B Testing
Experimentation at Spotify: Three Lessons for Maximizing Impact in Innovation
Coming Soon: Confidence — An Experimentation Platform from Spotify
Bringing Sequential Testing to Experiments with Longitudinal Data (Part 2): Sequential Testing