X open-sources 'For You' feed algorithm—here's how it works
X (formerly Twitter) just made its "For You" feed algorithm public, putting the full code on GitHub as of January 20, 2026.
The move is all about being more transparent and letting users see how their feeds are shaped—something a lot of people have been asking for.
What's actually going on behind your feed?
The "For You" feed uses a two-step system: Thunder ranks posts from accounts you follow, while Phoenix (powered by Grok) sorts out content from everyone else.
Together, they process billions of choices daily by looking at your last 128 interactions to guess what you'll like or ignore—everything from likes and replies to blocks and mutes.
Why does this matter for you?
By opening up the algorithm, X is aiming for fresher feeds that better match your current interests.
They're also promising regular updates explaining any changes. Plus, with the community able to review the code, it's easier to spot issues or suggest improvements.
This shift comes after Elon Musk called the old system "dumb" and pushed for big upgrades—so expect a smarter, more personalized scroll ahead.