Which product design innovation was instrumental in helping Spotify gain competitive advantage over other streaming services in the mid-2010s?

The music industry has undergone radical transformation through streaming platforms. Beyond changing how we consume music, these platforms have revolutionized product design principles in ways that extend far beyond just the interface. This trivia question focuses on a key product design innovation that fundamentally changed how streaming services operate and engage users, creating the personalized music experience we now take for granted.

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The Discover Weekly personalized playlist algorithm that analyzes listening patterns to recommend new music
The social sharing features allowing users to display their music on social media platforms
The freemium business model with ad-supported basic tier and premium subscription options
The integration of podcast content alongside music streaming in a single platform