Custom columns in AdWords can help marketers get more detailed insights into how their campaigns are performing based on non-standard metric targets. Now, advertisers can create and track custom metrics at the keyword and ad levels in addition to the campaign and ad group levels, which have been available since 2014.
As with just about every other new addition to the interface, this update is available only in the new AdWords “experience.”
Note that if you try to set up new custom columns or edit existing ones in the old AdWords interface, you’ll get a notice letting you know that the new columns won’t transfer over to the new AdWords interface. Just one more sign that the deprecation of the old UI is coming closer.