The plugins are available for free, however, they do require a corresponding Houdini Engine license. Interactive Houdini Core/Houdini FX and Houdini Indie licenses will also run these plugins in a license mode that corresponds to the license being checked out. (IE: A Houdini Indie license will allow the plugin to import Houdini Indie assets).

Houdini Engine for Unity and Unreal is a free commercial license that only supports Unity and Unreal

Houdini Engine is a paid license($525 USD for Workstation | $795 USD for Floating) that will support all official Houdini Engine plugins, Hython, Custom game engines and allow for batch processing and .usd file creation (in preparation for rendering with Karma)

Houdini Engine Indie is a free Houdini Engine license that is only compatible with Houdini Indie files and assets. This will support all official Houdini Engine plugins and allow for batch processing and .usd file creation (in preparation for rendering with Karma).

Houdini Engine Education is an included Houdini Engine license packaged with Houdini Education licenses. This will support all official Houdini Engine plugins and allow for batch processing and .usd file creation (in preparation for rendering with Karma).