Hello,
Thanks for reaching out. At the moment, the only way this would be possible to check the last modification time of a user list through the API would be by checking logged requests/responses or looking at the change history in the UI. However, you can use the
change event service to retrieve information about changes made to entities, including
campaign criteria (which include audience info).
The change event (and status) services do not support all entities that can found in the UI at the moment, but additional resource types are planned for future releases. You can follow our
Ads developer blog to stay up to date on such changes.
Regards,
Matt
Google Ads API Team

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