X’s May 2026 feed stack uses Grok-1 and Grox for ranking

This is a concrete map of how X’s recommendation feed is assembled: ranking, hydration, ad blending, storage, and moderation are split across named services rather than a single black box. For streaming and video teams, the relevant detail is that the document ties multimodal embeddings and real-time moderation directly into the feed path, not as a separate after-the-fact layer. It also shows how much of the system is expressed in Rust and Python across 207 source files. What to watch next: whether the repo’s later chapters, especially the Grox and Phoenix inference sections, add more detail on the 19 engagement weights and the 18 post-retrieval filters.