README

X's Recommendation Algorithm

X's Recommendation Algorithm is a set of services and jobs that are responsible for serving feeds of posts and other content across all X product surfaces (e.g. For You Timeline, Search, Explore, Notifications). For an introduction to how the algorithm works, please refer to our engineering blog.

 Architecture

Product surfaces at X are built on a shared set of data, models, and software frameworks. The shared components included in this repository are listed below:

| Type | Component | Description |
|------------|------------|------------|
| Data | tweetypie | Core service that handles the reading and writing of post data. |
|      | unified-user-actions | Real-time stream of user actions on X. |
|      | user-signal-service | Centralized platform to retrieve explicit (e.g. likes, replies) and implicit (e.g. profile visits, tweet clicks) user signals. |
| Model | SimClusters | Community detection and sparse embeddings into those communities. |
|       | TwHIN | Dense knowledge graph embeddings for Users and Posts. |
|       | trust-and-safety-models | Models for detecting NSFW or abusive content. |
|       | real-graph | Model to predict the likelihood of an X User interacting with another User. |
|       | tweepcred | Page-Rank algorithm for calculating X User reputation. |
|       | recos-injector | Streaming event processor for building input streams for GraphJet based services. |
|       | graph-feature-service | Serves graph features for a directed pair of users (e.g. how many of User A's following liked posts from User B). |
|       | topic-social-proof | Identifies topics related to individual posts. |
|       | representation-scorer | Compute scores between pairs of entities (Users, Posts, etc.) using embedding similarity. |
| Software framework | navi | High performance, machine learning model serving written in Rust. |
|                    | product-mixer | Software framework for building feeds of content. |
|                    | timelines-aggregation-framework | Framework for generating aggregate features in batch or real time. |
|                    | representation-manager | Service to retrieve embeddings (i.e. SimClusers and TwHIN). |
|                    | twml | Legacy machine learning framework built on TensorFlow v1. |

The product surfaces currently included in this repository are the For You Timeline and Recommended Notifications.

 For You Timeline

The diagram below illustrates how major services and jobs interconnect to construct a For You Timeline.

!

The core components of the For You Timeline included in this repository are listed below:

| Type | Component | Description |
|------------|------------|------------|
| Candidate Source | search-index | Find and rank In-Network posts. ~50% of posts come from this candidate source. |
|                  | tweet-mixer | Coordination layer for fetching Out-of-Network tweet candidates from underlying compute services. |
|                  | user-