Reel Friends: Building Social Discovery that Scales to Billions (opens in new tab)
Friend Bubbles may look like a simple Reels feature, but building it required substantial engineering work. The feature surfaces Reels that friends have watched or reacted to, relying on an evolving machine-learning model and platform-specific behavior. Meta engineers explain that a key, unexpected discovery ultimately helped make the experience work. ### What Friend Bubbles Does - Highlights Reels that a user’s friends have watched or reacted to. - Connects social activity with Reels recommendations in a more visible way. ### Engineering Challenges - The team had to evolve the machine-learning model powering the feature. - iOS and Android users exhibited different behaviors, requiring the team to account for platform-specific usage patterns. - The feature’s apparent simplicity concealed complex recommendation and product-engineering challenges. ### Podcast Discussion - Meta Tech Podcast host Pascal Hartig speaks with Facebook Reels engineers Subasree and Joseph. - They discuss the model’s development, differences between mobile platforms, and the surprising insight that helped the feature succeed. - The episode is available through Meta’s podcast channels and services including Spotify, Apple Podcasts, and Pocket Casts. The episode illustrates why seemingly straightforward social features can demand deep experimentation, modeling, and cross-platform engineering.