Google is changing the default behavior of Demand Gen Lookalike segments so they act as hints for its systems instead of hard limits. Search Engine Land’s Anu Adegbola reported the plan on October 12. The report gives no date for when the default flips.
Under a constraint, delivery stays inside the chosen Lookalike audience. In suggestion mode, Google’s systems treat that audience as a starting point and may reach beyond it. Advertisers who want the old behavior can opt out and keep segments as a targeting constraint, per a Google help page on that setting.
Lookalikes come from first-party data: site visitors, app users, YouTube audiences, and customer lists, in three size options. A segment needs over 100 matched users who are active, and Google refreshes audiences on a one-to-two-day cycle.
Wider reach is not automatically better. Track conversion quality, acquisition cost, and customer value, and decide before the default lands whether your accounts need the constraint.
Search Engine Land, Anu Adegbola, October 12, 2026.
