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Navigate Google’s New Rule on Duplicate Lookalike Lists

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Written by

shivamcrushpressai

in

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I recently discovered an important update from Google affecting how I run Demand Gen campaigns using Lookalike user lists. Starting April 30, Google will block creating duplicate Lookalike lists via the Google Ads API and return an error code for any breaches.

This update might seem quiet, but its implications are significant, especially for those of us utilizing automated systems or third-party tools. Google is now enforcing a uniqueness check to prevent duplicates that have identical seed lists, expansion level, and country targeting.

Why do I care about this change? An unaddressed error could disrupt the workflow of my campaigns if I don’t update my integrations in time.

Here’s what I plan to do:

  • Audit my current Lookalike lists and reuse those that already align with my goals instead of creating new ones.
  • Update my API error handling processes to catch the new DUPLICATE_LOOKALIKE error code in versions v24 and above, or RESOURCE_ALREADY_EXISTS in older versions.

The bottom line is, while this change is housekeeping, the deadline is firm. I need to ensure my campaigns are technically prepared before the end of April to maintain stability in Google’s systems.

If you’re interested in a deeper dive, I highly recommend checking out Google’s blog post detailing these changes: Upcoming changes to Lookalike user lists in the Google Ads API, starting April 30, 2026.

Inspired by this post on Search Engine Land.

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FAQs

What is changing for duplicate Lookalike lists in the Google Ads API?

Starting April 30, Google will block the creation of duplicate Lookalike lists through the Google Ads API. Duplicate lists are identified when they use the same seed lists, expansion level, and country targeting.

Which campaigns are affected by this Google Lookalike list update?

The post discusses the impact on Demand Gen campaigns that use Lookalike user lists. It is especially relevant for advertisers using automated systems or third-party tools to create those audiences through the API.

What error codes should Google Ads API integrations handle?

Integrations should catch the new DUPLICATE_LOOKALIKE error code in Google Ads API versions v24 and above. Older versions may return RESOURCE_ALREADY_EXISTS instead.

How should advertisers prepare before the April 30 deadline?

The author plans to audit existing Lookalike lists and reuse lists that already match campaign goals instead of creating new duplicates. They also plan to update API error handling so campaign workflows are not disrupted.

Why does Google’s uniqueness check matter for automated PPC workflows?

If an automation or third-party tool keeps trying to create duplicate Lookalike lists, the API can return errors that interrupt campaign workflows. Preparing integrations ahead of the deadline helps maintain stability in Google Ads systems.

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