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There are no plans to end of life 3DF. A large percentage of our Visualize partners use this interface, and we will continue to support it. In addition, as we add new functionality we will provide it in both APIs, such as adding Physically Based Rendering.
An HSF (HOOPS Stream File format) created by the HPS API is not compatible with 3DF. However, an HSF created by 3DF can be read by HPS.