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I understand that you would like to know the details about connecting ExpressRoute Gateway circuit to ExpressRoute Gateway(s) across different tenants.
Yes, customers can authorize ExpressRoute connection across tenants.
See : FAQ ExpressRoute
There are no limitations based on the SKU of the Public IP of an ExpressRoute Gateway.
Instead, the limitations apply based on the SKU of the ExpressRoute Gateway itself.
So you should be a able to connect the Gateways to the circuit without any issue.
Kindly let us know if this helps or you need further assistance on this issue.
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