The January 2026 release: X open-sources its live algorithm
On January 20, 2026, X Engineering open-sourced the production For You feed algorithm at xai-org/x-algorithm — a ground-up rewrite ranked by Phoenix, a transformer built on the same architecture as xAI's Grok, with a stated commitment to public updates roughly every four weeks. Unlike the partial 2023 snapshot, this was published as the live system.
Browse the initial release tree on GitHub ↗aaa167b
What shipped
The initial release contained four components: Home Mixer, the Rust orchestration layer that assembles the For You feed; Thunder, the in-network candidate source serving posts from accounts you follow; Phoenix, the Grok-based transformer handling both out-of-network retrieval and the ranking of everything; and the candidate-pipeline framework that composes them. Grox — the content-understanding and safety layer — and the ads module were not part of this release; both arrived in May.
The initial January 20, 2026 release (commit aaa167b) contained Home Mixer, Thunder, Phoenix, and the candidate-pipeline framework; the Grox content-understanding service and the home-mixer/ads module were not yet included, and the weighted scorer's numeric parameters were absent from the very first commit.
For You candidates come from two sources: Thunder (in-network — posts from accounts you follow) and Phoenix Retrieval (out-of-network — ML-based similarity search across a global corpus). Both are ranked together by Phoenix.
Why this was different from 2023
Twitter's March 2023 open-sourcing was a curated snapshot of a Scala codebase — real, but partial, never meaningfully updated, and frozen the day it was published. The January 2026 release was framed by X Engineering as the production system itself, built on the same transformer architecture as Grok, and accompanied by a commitment that mattered more than the code: updates roughly every four weeks, with developer notes.
In January 2026, X Engineering open-sourced its production For You feed algorithm at xai-org/x-algorithm, built on the same transformer architecture as xAI's Grok model.
X has stated the open-source algorithm repository will be updated roughly every four weeks, with developer notes describing what changed.
The design break: no more hand-engineered features
The launch README stated the philosophy in one line that invalidated most existing X-growth advice: every hand-engineered feature and most heuristics were eliminated. Relevance is learned by the transformer from each user's engagement history — not assembled from the manually constructed feature pipelines that the famous 2023 weight tables belonged to. That sentence has been in the README since day one of this repository.
The current X algorithm has eliminated every hand-engineered feature and most heuristics; the Grok-based transformer learns relevance from the user's engagement history.
What was withheld from the start
One omission is worth recording precisely, because it scopes every reach claim made since: the weighted scorer — present in this very first release — references its numeric weights from a parameters module that was not included, and still has not been. Anyone who quoted "current X algorithm weights" after January 20, 2026 was not reading them from this repository.
What this means for you
The launch reset the evidentiary baseline for the entire X-optimization field. From this date forward, "the algorithm does X" is a checkable claim against living code rather than an appeal to a 2023 fossil — and that is the standard every page on this site holds itself to. If you read one thing from this release, read the design break above: strategies built on gaming individual hand-tuned signals belong to the old system.