Reel Friends: Building Social Discovery that Scales to Billions

Meta's Facebook Reels team engineers discuss building the Friend Bubbles feature for discovering social content at scale.

• •Friend Bubbles highlights Reels that friends have watched and reacted to
• •The feature required significant engineering work despite appearing simple on the surface
• •The team evolved the machine learning model powering the feature
• •They discovered different behavioral patterns between iOS and Android users
• •A key technical discovery enabled the feature to work effectively at billion-scale

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