Hello Xinyi,
Thanks for getting back to us.
According to this guide, avg_monthly_searches will only provide an averaged for the past 12 months. Since you've mentioned that the Keyword Planner tool is possible to pull search volume of all available months for almost 4 years, allow me to raise a feature request for this instead (subject for review). Since there is no guarantee if this will be supported in the API soon, we recommend that you keep an eye to our blog for updates and new releases.
Regards,
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Mark Kevin Albios |
Google Ads API Team |
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