Edit: it should be available or will be available very shortly. It requires OneStream 8.2. You might want to discuss licensing requirements with your Customer Success Manager.
Going to be testing it in a few days to determine what functionality it gives over standard Rest API connector to determine if it's worth it. There are already ways to accomplish this without a built in connector.
We are going to just do data management extracts to load to PowerBI. The OneStream connector still has to refresh from what we were told, so to save the connector cost we are just doing extracts. Not sure what we are missing out on, but it doesn't seem like anything.