Google is updating how Lookalike segments work in Demand Gen campaigns, moving the default setting from strict targeting to a suggestion mode.
Lookalike segments, built from first party seed lists such as Customer Match, website visitors, app users, or YouTube viewers, will now guide delivery rather than act as a targeting constraint. This gives Google more flexibility to expand reach beyond closely matched profiles.
Advertisers who prefer the previous behavior can opt out using a dedicated form and keep Lookalike segments as a Targeting Constraint in their campaign settings.
Here’s the official help article found by Dario Zannoni: Use Lookalike segments in Demand Gen campaigns as a Targeting Constraint.