Support for 'instances' metric in Data Warehouse API (API 1.4)

[#1]

We're attempting to use the Analytics API to retrieve a data warehouse report that includes the 'instances' metric. Though we can run the report through the user interface, we cannot run the report through the API. 

We're met with the following error: Exception: Metric "instances" not supported in warehouse requests.

Please let me know if I can provide any more detail!