Hello db042190,
An on-premises data gateway is required when one or more Azure Analysis Services servers in the same region connect to on-premises data sources.
If your data source is not connecting to on-prem, you don't need an on-prem gateway.
To answer your question: AAS needs a gateway only when connecting to the on-prem DS.
The document you have referenced in your comment mentioned the same:
"Gateway software acts like a bridge; it allows organizations to retain databases and other data sources on their on-premises networks and access that on-premises data in cloud services, such as Power BI and Microsoft Azure Analysis Services.
A gateway facilitates quick, behind-the-scenes communication that flows from a user in the cloud to your on-premises data source and then back again to the cloud."
I hope this clarifies your question. Please let me know if you have any further questions.
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