What triggers it
A bid strategy enters a Learning status in four documented cases: the strategy was recently created or reactivated; a setting for the strategy was changed; campaigns, ad groups or keywords were added to or removed from it; or, on Shopping campaigns, certain ad group target changes. Notably, changing a campaign's budget is not among Google's listed triggers, despite being the change advertisers most often avoid for fear of "resetting learning".
How long it lasts
Google says calibration can take up to three weeks, or one to two conversion cycles, and can be faster with more conversion data. That makes it far more painful in B2B than in high-volume ecommerce: low conversion counts and long sales cycles both stretch the window. The practical response is to batch significant changes together rather than spread them across a week, which is Google's own Smart Bidding guidance. We break down the full trigger list in what actually puts a Google Ads campaign into learning.