From Houdini 18.5
What Houdini Engine license do I need?

Houdini Engine for Unity/Unreal provides free commercial licenses for the UE5 and Unity plug-ins only.

For all other host applications, including proprietary plug-ins, and for Batch processing on the farm, commercial Houdini Engine licenses are available for rent. These licenses are also available as volume rentals for medium and large studios.

License Cost Asset Types Houdini GUI UE5 Plug-in Unity Plug-in Maya/Max Plug-in Batch Processing
Houdini Engine for Unity FREE .HDA x YES YES x x
Houdini Engine for UE5 FREE .HDA x YES YES x x
Houdini Engine $$ .HDA x YES YES YES YES
Houdini Engine Indie FREE .HDALC/.HDA x YES YES YES YES