How can I retrieve a new address extension attribute on checkout?

I have created a modal for request customer to update her address, because we have do an migration and need force customer to update her address.

So, after create an endpoint for update address by API (for that what modal can do an dynamic request for that what not refresh the page) i have created an new extension attribute called “is_address_updated” for store when customer update manually their address.

So, for show the modal or not in checkout page (on select address), i need retrieve this new attribute for the “knockout”.

How can I do this?

Thank you since now