On AUD, you earn interest on cash sitting in your AUD Wallet (the Macquarie Cash Management account). You can see interest paid by Macquarie here.

Effective from 9 April, on USD, there is no interest earned on your accounts.  One of the way Stake keeps the lights on is by earning interest on the cash sitting in the USD accounts. This helps cover our costs and allows us to bring you $0 brokerage and a better trading experience.