X open-sources For You feed recommendation algorithm

RPRohan Paul@rohanpaul_ai

X has released the latest "For You" feed algorithm to GitHub. Moving the feed closer to a Grok-style AI ranking system than a rule-heavy social media sorter. The system first gathers posts from accounts you follow through Thunder, then adds outside posts through Phoenix, which searches for content that looks relevant even if you do not follow the author. Ranking now behaves less like a checklist of likes, reposts, and keywords, and more like a transformer model that reads the user, the post, and past behavior as one prediction problem. Instead of asking “is this post good,” the model predicts multiple possible actions, such as whether you might reply, like, repost, watch, or skip. Thunder is the fast “people you follow” system. It keeps a live memory-store of recent posts, replies, reposts, and videos from users, then quickly pulls posts from accounts you follow when your For You feed is built. It is basically the in-network candidate source. Phoenix is the AI recommendation system. It has 2 jobs: first, Phoenix Retrieval finds outside posts from the global X corpus using similarity search, and then Phoenix Ranking scores both followed-account posts and outside posts using a Grok-based transformer model.