Google acknowledged that Performance Max (PMax) campaigns can be controlled through API placement exclusions — contradicting months of its own documentation and support guidance, according to new research from ad tech firm Optmyzr.
This revelation gives advertisers more programmatic control over their PMax campaigns than previously thought possible, potentially saving significant time and resources in campaign management.
The big picture. Performance Max campaigns, Google’s AI-driven ad format, have been a source of frustration for advertisers seeking more granular control over where their ads appear.
Lead up. Earlier this year we saw that despite Navah Hopkins, Brand Evangelist of Optmyzr, reporting that Google said that API based placements exclusions don’t work for PMax campaigns, multiple advertisers were reporting the opposite.
By the numbers. Optmyzr ran an experiment, running from Dec. 30 to Jan. 21. It showed:
- Zero ad spend on excluded placements after implementing API controls.
- Complete effectiveness of API-based exclusions, despite Google’s previous claims.
- Faster implementation compared to manual UI controls.
Behind the scenes. Google’s documentation and AI help center had explicitly stated that placement exclusions would only work through their user interface, not via API.
- Multiple support channels reinforced this incorrect guidance.
- This misinformation was shared for months.
- Google has since updated its stance after Optmyzr’s findings.
What they’re saying. Following the experiment, Google admitted that placement exclusions work through both the API and UI as we see in this response from Ginny Marvin, Google Ads Liaison:
Why we care. Performance Max campaigns represent a significant portion of many advertisers’ Google Ads spend, but the lack of control over where ads appear has been a major pain point. This situation also highlights a broader point: you shouldn’t take platform limitations as gospel, even when they come directly from Google. Testing and verification could reveal hidden capabilities that provide competitive advantages.
Bottom line. This discovery highlights a broader issue in ad tech: platform documentation doesn’t always reflect actual capabilities, requiring advertisers to actively test and verify functionality.
What’s next. As advertisers, you should:
- Review your PMax campaign controls.
- Consider implementing API-based exclusions for more efficient management.
- Maintain active oversight despite automated controls.
- Confidently question capabilities you may have strong reason to believe isn’t true.
Between the lines. The finding suggests other undocumented capabilities might exist across Google’s ad platforms, encouraging advertisers to question and test official limitations.
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