Right now (4th February 2025) it’s impossible to create a form with progressive fields from a Custom Object.
This limitation affects in my company, we work with some custom objects and this feature will be really helpfull for us.
Please consider to add progessive fields in all objects, not just “contacts”.
Visitor identification is linked to the contact object, not associated custom objects.
The HubSpot website code needs to be able to see the properties on the contact record for an identified visitor in order to know if there is already data in these fields.
This would require the web code being able to go from analytics profile → Contact Record → Associated Custom Object → Property.
But if there are multiple records in your custom object that are associated to the contact record, then which one do you use for progressive profiling?
In short, it’s not a simple fix, so you might need to find a way to use contact record properties and try and find a way to push these across to the associated custom object record.
Factor in that new HubSpot forms don’t offer progressive profiling and it’s not clear if there is a plan to. Therefore I wouldn’t expect HubSpot to be developing new functionality for progressive profiling on legacy forms (unless they also start offering progressive profiling on the new forms).