api – Can I set MSI stock values using products REST endpoint?

We currently run Magento without MSI. The ERP sends stock updates via extension attributes on the (bulk) product endpoint. This enables us to do most product updates in on API call. Very convenient.

We are looking to implement MSI, but it seems it is not possible to set multiple source quantities as product extension attributes and we would need to start making two API calls (maybe more) to create a product and assign some stock….

We would like to continue to do a single API call to create/update product AND set the stock in MSI like so:

{ 
"product" : {
    "sku": "24-MB01-3",
    "name": "My Duffle Bagz 3",
    "attribute_set_id": 15,
    "price": 34,
    "status": 1,
    "visibility": 4,
    "type_id": "simple",
    "extension_attributes": {
        "category_links": (
            {
                "position": 0,
                "category_id": "3"
            },
            {
                "position": 0,
                "category_id": "4"
            }
        ),
        {
        "sourceItems": (
         {
               "sku": "24-MB01-3",
               "source_code": "NW",
               "quantity": 1000,
               "status": 1
         },
         {
             "sku": "24-MB01-3",
             "source_code": "LN",
             "quantity": 500,
             "status": 1
         })
       }
    }
}
}

Because we use bulk endpoints, our current process is asynchronous, so knowing when a particular product is created and we can then set the stock is difficult.

Is there any way to do this rather than having to use the separate source-items endpoint?