Finally able to see how the "For You" algorithm works behind the scenes, Phoenix Transformer unified scoring + diversity adjustment, with full technical details, so the community can thoroughly audit it.

Platform X open-sourced the latest recommendation algorithm for the For You feed on May 15, which integrates content from followed accounts and content discovered through similarity search, using the Grok architecture's Phoenix Transformer for unified scoring.
The algorithm analyzes recent interactions and predicts the probabilities of likes, replies, and shares, providing a final relevance score; the ranking process includes candidate collection, context augmentation, scoring, and diversity adjustment.
The open-source release offers a runnable pipeline, pre-trained models, content understanding services, and an ad blending module, all primarily driven by Transformers.