Google Ads · Status at source date: Newsletter archive
Google Ads API will block duplicate Lookalike lists from April 30
Google has announced a uniqueness check for Lookalike user lists in the Google Ads API, effective April 30, 2026. The enforcement primarily targets Demand Gen campaigns, where automated systems have generated duplicate audience lists sharing identical seed lists, expansion levels, and country targeting: consuming system resources without delivering distinct signal value.
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What changed
From April 30, any API attempt to create a list that matches an existing list on all three attributes will return a DUPLICATE_LOOKALIKE error in v24 and above, or RESOURCE_ALREADY_EXISTS in earlier versions. Existing lists are unaffected and can continue to be used in campaigns. The recommended response is to audit current Lookalike configurations and consolidate duplicates before the deadline.
The change is narrowly scoped and will be invisible to most advertisers who manually build Lookalike lists. It is primarily relevant to developers and tool vendors who create lists programmatically.
Why it matters for advertisers
For you, this means checking your API integrations if you generate Lookalike lists at scale and updating your error-handling logic before April 30.
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Original newsletter text and archive evidence
Google Ads API will block duplicate Lookalike lists from April 30
Google has announced a uniqueness check for Lookalike user lists in the Google Ads API, effective April 30, 2026. The enforcement primarily targets Demand Gen campaigns, where automated systems have generated duplicate audience lists sharing identical seed lists, expansion levels, and country targeting: consuming system resources without delivering distinct signal value.
From April 30, any API attempt to create a list that matches an existing list on all three attributes will return a DUPLICATE_LOOKALIKE error in v24 and above, or RESOURCE_ALREADY_EXISTS in earlier versions. Existing lists are unaffected and can continue to be used in campaigns. The recommended response is to audit current Lookalike configurations and consolidate duplicates before the deadline.
The change is narrowly scoped and will be invisible to most advertisers who manually build Lookalike lists. It is primarily relevant to developers and tool vendors who create lists programmatically.
For you, this means checking your API integrations if you generate Lookalike lists at scale and updating your error-handling logic before April 30.
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