If you look at the data on a log scale, and include other stack exchange sites, it's apparent that the serious decline is starting after ChatGPT launches: https://x.com/CraigGidney/status/2115664509042053377/photo/1

One way that stackoverflow does stand out from the other stackexchange sites is that its half life appears far shorter. On a log scale plot it has a steeper descent than the other stackexchange sites. I'm not sure what to make of that. Another interesting thing is that the math stackexchange initially declines more slowly than the others for a year or two and then decays pretty similarly. You can also see examples in some of the other sites of their decay beginning before chatgpt releases (e.g. drupal). You can also see some sites decaying a decade earlier (e.g. expressionengine). I think those outliers are from their subject being too specific and going out of style.

I got the cross-site data from data.stackexchange.com with this vibe-coded query:

    DECLARE @sql NVARCHAR(MAX) = N'
    SELECT
      site = [$site_name$],
      month = DATEADD(MONTH, DATEDIFF(MONTH, 0, CreationDate), 0),
      questions = COUNT(*)
    FROM PostsWithDeleted
    WHERE PostTypeId = 1
    GROUP BY DATEADD(MONTH, DATEDIFF(MONTH, 0, CreationDate), 0)
    ';

    EXEC dbo.sede_ineachdb
      @SQLCommand = @sql,
      @IncludeMainSites = 1,
      @IncludeMetaSites = 0,
      @IncludeMainMeta = 0;