All content that appears in Facebook and Instagram feeds — posts, Reels, Stories, suggested accounts, Explore — is ranked by AI systems that predict what each user is most likely to engage with.

Meta published 22 AI system cards (14 Facebook, 8 Instagram) in June 2023 detailing each algorithm. Instagram Reels: retrieval → lightweight model (~100 reels) → integrity filters → final ranking. Instagram video time up 20%+ YoY globally (Q2 2025). Instagram Explore: up to 1,500 media via collaborative filtering, personalized PageRank, two-tower sparse networks → early/late ranking. Meta's DLRM (2019) → Generative Recommenders (HSTU architecture, 2024) → 1.5 trillion parameter models now deployed. Controversies: Haugen testimony that 2018 'meaningful social interaction' algorithm change increased divisive content; Mozilla Foundation (2023) criticized system cards as incomplete.