A quiet but important change is coming to the Google Ads API that will affect how advertisers and developers create Lookalike user lists, especially for Demand Gen campaigns.

What’s changing. Google will enforce a uniqueness check on Lookalike user lists, blocking duplicate lists with the same seed lists, expansion level, and country targeting. Attempts to create a duplicate will return an API error after April 30.

Why we care. If you use automated scripts or third-party tools to generate audience lists, an unhandled error could quietly break your campaign workflows if you don’t update integrations in time.

What you need to do.

  • Audit existing Lookalike lists and reuse ones that already match your intended configuration rather than creating new ones
  • Update your API error handling to catch the new DUPLICATE_LOOKALIKE error code in v24 and above, or RESOURCE_ALREADY_EXISTS in earlier versions

Bottom line. This is a housekeeping change to keep Google’s systems stable, but the April 30 deadline is firm. If you manage campaigns programmatically, treat this as a technical to-do before the end of April.

Google’s announcement. Upcoming changes to Lookalike user lists in the Google Ads API, starting April 30, 2026

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Anu AdegbolaAnu Adegbola

Anu Adegbola has been Paid Media Editor of Search Engine Land since 2024. She covers paid search, paid social, retail media, video and more.

In 2008, Anu started her career delivering digital marketing campaigns (mostly but not exclusively Paid Search) by building strategies, maximising ROI, automating repetitive processes and bringing efficiency from every part of marketing departments through inspiring leadership both on agency, client and marketing tech side. Outside editing Search Engine Land article she is the founder of PPC networking event – PPC Live and host of weekly podcast PPC Live The Podcast.

She is also an international speaker with some of the stages she has presented on being SMX (US, UK, Munich, Berlin), Friends of Search (Amsterdam, NL), brightonSEO, The Marketing Meetup, HeroConf (PPC Hero), SearchLove, BiddableWorld, SESLondon, PPC Chat Live, AdWorld Experience (Bologna, IT) and more.