Upcoming changes to Lookalike user lists in the Google Ads API, starting April 30, 2026
Google Ads is committed to providing a reliable and efficient environment for all advertisers. To ensure that our systems remain stable and that resources are allocated fairly, we are introducing a uniqueness check for Lookalike user lists that prevents the creation of duplicate lists. These changes primarily impact Demand Gen campaigns and will begin to be enforced starting on April 30, 2026.
A Lookalike user list is considered a duplicate if it shares all of the following attributes with an existing list:
- Seed lists: The underlying source audiences used to build the Lookalike.
- Expansion level: The degree of similarity to the seed lists.
- Country targeting: The geographical reach of the Lookalike list.
If an advertiser attempts to create a duplicate list after April 30, 2026, the Google Ads API will return the error code DUPLICATE_LOOKALIKE for v24 and beyond. For earlier versions, the error will be RESOURCE_ALREADY_EXISTS. What this means for you
For the majority of advertisers, these changes will go unnoticed, as most current usage falls well within these new boundaries. However, to ensure a smooth transition, we recommend the following:
- Reuse audiences: Instead of creating a new, identical Lookalike list, verify if an existing one with the same configuration can be reused in your campaigns.
- Update error handling: If you use the Google Ads API, ensure your integrations are prepared to handle the new error starting on April 30, 2026: v24 will return the DUPLICATE_LOOKALIKE error code and all previous versions will return RESOURCE_ALREADY_EXISTS.
If you have any questions or want to discuss this post, please reach out to us on our “Google Advertising and Measurement Community” Discord server.
