In addition to trials, there are three other pricing tiers for different licenses types. The Apprentice download option contains assets for non-commercial use. Apprentice files are tied to that license and convert any Houdini instance into a non-commercial session. To use assets commercially, buyers must purchase the commercial or studio version of the asset and have a commercial license of Houdini or Houdini FX. Any assets opened in Houdini Apprentice will be non-commercial.
Authors have full control over Apprentice, Commercial and Studio pricing. Separate pricing allows authors to sell to hobbyists to professional firms alike.