The original v1 of the Forms API was released in sync with the launch of our then new form tools. Since then, we've added several new features to our forms, including support for progressive and dependant fields, support for inline thank you messages, and new styling options for columns and rows of fields. To prevent issues with breaking changes to the API, these features were not added to the v1 Forms API, and the v2 API was released with those new features. As a result, the v1 API is no longer feature complete with the HubSpot forms tools.
On March 29th, 2019, the v1 Forms API will be sunset. This will include all endpoints beginning with the /forms/v1/ path. At this point, the /forms/v1/ endpoints will no longer function. Integrations using the v1 endpoints will need to be updated to use the current v2 endpoints.
The v1 API and the v1 endpoints will be shut down on March 29th, 2019.
Note: This sunset specifically affects endpoints beginning with /forms/v1/. This will not include the new /form-integrations/v1 endpoint to get form submissions.