# 85: Reel Friends: Building Social Discovery that Scales to Billions

Page: https://stenobird.com/podcast/meta-tech-podcast-525691/85-reel-friends-building-social-discovery-that-scales-to-billions
Text version: https://stenobird.com/podcast/meta-tech-podcast-525691/85-reel-friends-building-social-discovery-that-scales-to-billions.md
Podcast: [Meta Tech Podcast](https://stenobird.com/podcast/meta-tech-podcast-525691)
Published: 2026-05-08T16:04:00+00:00
Episode link: https://insidefacebookmobile.libsyn.com/85-reel-friends-building-social-discovery-that-scales-to-billions
Audio file: https://traffic.libsyn.com/secure/insidefacebookmobile/mtp85_rc2.mp3?dest-id=697376
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JSON: https://stenobird.com/v1/public/podcasts/meta-tech-podcast-525691/episodes/85-reel-friends-building-social-discovery-that-scales-to-billions
Duration seconds: 2314

## Resource

You've probably spotted those little circles of your friends' faces popping up on Facebook Reels. They look simple enough, but building them was a proper engineering challenge. In this episode, Pascal chats to Joseph and Subasree about Friend Bubbles, a feature that surfaces which of your close friends have been watching and reacting to the same Reels as you. We get into the details of how prefetching keeps things snappy without wrecking scroll performance, why the team's ML model had to move from survey-based friend rankings to real-time interaction signals, and the surprising discovery that showing fewer bubbles actually made the whole feature click. If you've ever underestimated a "simple" feature, this one's for you. Got feedback? Send it to us on Threads ( https://threads.net/@metatechpod ), Instagram ( https://instagram.com/metatechpod ) and don't forget to follow our host Pascal ( https://mastodon.social/@passy , https://threads.net/@passy_ ). Fancy working with us? Check out https://www.metacareers.com/ . Links https://engineering.fb.com/2026/03/18/ml-applications/friend-bubbles-enhancing-social-discovery-on-facebook-reels/ https://engineering.fb.com/2026/04/21/ml-applications/modernizing-the-facebook-groups-search-to-unlock-the-power-of-community-knowledge/ Timestamps Intro 0:06 Meet the Engineers: Backgrounds and Roles 1:53 Goals and Aspirations in Video Recommendations 4:20 The Origin of Friend Bubbles 4:41 Defining Success: Metrics and User Experience 5:40 Client-Side Constraints and Challenges 6:57 Feature Description: What Are Friend Bubbles? 8:31 Initial Challenges and Performance Issues 9:29 Architectural Changes for Performance 11:34 Impact of Performance on User Experience 15:14 Addressing Client-Side Challenges 16:58 Model Development: From Surveys t…

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