I’ve learned that it’s not uncommon for hosts to provide discounts, even on top of the monthly discount, when asked. Especially for multi-month stays. The last place I stayed I messaged two places in the same price range and with similar amenities: “I’m interested in booking for 3 months. Do you have any additional discounts available?” One host declined, the other offered a 30% discount with no additional haggling, and my dates were during high season.
In my limited experience it seems to be more successful with people who are managing their own property and would be happy for the guaranteed income and reducing the overall hassle. I haven’t had any success with professional hosts that are doing this as their full-time job and managing other people’s property.