Since "Jan 8 at (more or less) 19:57" the predictor or Tag Future Report hasn't been updated. This could screw more than one Recommended/Interesting tabs of Stack Overflow users. How often does this script run? Will not run anymore? Why it isn't running? When will it start predicting again?

  • What is this thing..? Could someone link to it? Aug 19, 2014 at 3:47
  • @900sit-upsaday That's pretty neat. Thanks! Aug 19, 2014 at 5:03
  • I suspect the data is old. A friend of mine on RPG.SE has recently undergone a shift in topics: the predictor thinks he's uninterested in a tag he's recently been fairly active in, and interested in a tag he now participates in not often at all. Aug 19, 2014 at 5:07
  • I predict they are going to replace this whole thing that was just an experiment, probably not a successful one. Aug 19, 2014 at 6:25
  • It is not enabled on all sites - how well it works varies hugely depending on the nature of the site - and AFAIK it is not enabled on any meta sites, including meta.SE. Aug 22, 2014 at 14:33
  • mm... in SO is enabled but since Jan 8 hasn't been updated, why? stackoverflow.com/users/tag-future/79206
    – Braiam
    Aug 22, 2014 at 14:36
  • @Braiam let me check... Aug 22, 2014 at 14:36
  • @Braiam I didn't even know this existed. Thanks for posting this!
    – elixenide
    Aug 25, 2014 at 15:27

1 Answer 1


That's a slightly confusing sentence I guess. My bad.

What "X of their answers could have been considered when the predictor was last updated Y" means is really "when we last trained our prediction engine on Y, they had X answers."

That's reported because making a prediction when we have a ton of old user data is less impressive than we had relatively little.

The actual output of the prediction engine rolls over every couple of hours, and incorporates new answers.

Another way to think of it:

  • There is a Stack Overflow Prediction Engine Binary™ sitting on a server somewhere
    • this binary was last updated on Jan. 8th
    • accordingly, it was generated based on all available user data as of Jan. 8th
  • Every couple of hours, the binary is run against all active users and the results cached*
  • Whenever a user loads the homepage, those cached results are used to customize it

As to why the binary is so old, we're in the process of moving to a new ML backend service. Once we're on it the binary will be automatically retrained, the results available for more purposes than just the homepage. This is taking a longer than I had hoped.

Since a replacement is in the works, and the actual model represented by the binary changes very slowly, I've put off retraining for a while. It's a terribly manual process right now unfortunately.

*Greatly simplifying how this works, but the effect is basically the same

  • MM... through that doesn't explain why people that haven't touched in years a php question still see php as preferred tags, but I presume that's another bug report.
    – Braiam
    Aug 26, 2014 at 21:23
  • 2
    Any updates on the new ML backend?
    – Braiam
    Dec 29, 2015 at 21:13
  • 1
    From the future, ML backend, did it update itself?
    – Braiam
    Feb 24, 2017 at 19:52
  • 1
    This is the same engine that tag suggestions use?
    – Braiam
    Jul 6, 2021 at 21:35

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