Version history
What shipped, and when.
Public algorithm updates from the x-algorithm repository. Production defaults in this digest track the latest release.
- 2026.08.13Current
Weights, filters, and production Phoenix
Largest transparency drop since May. Publishes the live blending weights, visibility-filtering code, production Phoenix training, SimClusters retrieval, and the Under the Hood report jobs.
- Scoring weights. home-mixer/params/param.rs now carries production defaults used to blend Phoenix action probabilities into a single score.
- Visibility filtering. visibility-filtering/ decides allow, interstitial, or drop from labels, blocks, mutes, and viewer settings.
- Label producers. botmaker, scarecrow, agatha, bdsm, user-cred-v2, media-model-proxy, clip, and abuse-enforcement-service are in-tree.
- Phoenix training. Demonstration model replaced with production training + synthetic data so a proof-of-concept run is possible.
- SimClusters. Additional out-of-network source queried alongside Thunder and Phoenix retrieval.
- Under the Hood. Daily jobs and serving columns that power the per-account label transparency report.
- 2026.07.24
Mutual-follow reply boost settles at +15
After A/B tests at 5 / 10 / 15 / 20 and a brief 20 rollout, the bidirectional follow reply boost is set to 15. Dwell boost stays at 0.
- Bidirectional reply boost. Original posts from people you mutually follow add +15 to the reply head. Replies and reposts are not eligible.
- Why 15, not 20. Feedback during the World Cup: a 20 boost over-indexed on mutual follows and hid too much out-of-network conversation.
- 2026.07.13
Mutual-follow boost ships broadly
Boost of 20 rolled to many users while 0 / 5 / 10 / 15 continued as experiments. BidirectionalFollowHydrator added to Home Mixer.
- Hydrator. home-mixer/candidate_hydrators/bidirectional_follow_hydrator.rs checks SocialGraph for followed-by on in-network authors.
- 2026.07.10
Mutual-follow A/B test starts
Small percentage of traffic assigned reply-boost values of 5, 10, 15, or 20. Control remains 0.
- Experiment. Documented in docs/BIDIRECTIONAL_BOOST_CHANGE.md as the template for how param diffs will appear.
- 2026.05.15
First large code expansion
187 files changed, more than 18,000 lines. Rust/Python rewrite of the recommendation path continues to replace the 2023 Scala dump.
- Rewrite. Home Mixer, Thunder, Phoenix serving, and candidate pipeline land as the inspectable request path.
- 2026.01
x-algorithm repository opens
xAI publishes the Grok-powered For You stack at github.com/xai-org/x-algorithm, replacing the 2023 partial Twitter release. Public updates promised on a four-week cadence.
- Scope. In-network Thunder + Phoenix retrieval/ranking. Heuristic feature engineering largely removed in favor of the transformer.