A reminder that all Hacker News posts and comments are available on BigQuery and can be queried for free: https://console.cloud.google.com/marketplace/details/y-combi... (the `full` table is up-to-date; ignore the others)

Here's a query for a rough reproduction of what's asked in the title:

    WITH whoishiring_threads AS (
      SELECT id FROM `bigquery-public-data.hacker_news.full`
      WHERE `by` = "whoishiring" 
      AND REGEXP_CONTAINS(title, "Ask HN: Who is hiring?")
    )

    SELECT FORMAT_TIMESTAMP("%Y-%m", `timestamp`) as year_month,
    COUNT(*) as num_toplevel_posts
    FROM `bigquery-public-data.hacker_news.full`
    WHERE parent IN (SELECT id FROM whoishiring_threads)
    GROUP BY 1
    ORDER BY 1

Which results in something like this: https://docs.google.com/spreadsheets/d/13yGlJzFpVzZ-WNHAOsdo...

Still a bit of room to clean up the query, though, and there are some differences from the chart in the post.