Every Sketchfab user, regardless of membership, has the ability to download select 3D models.
A 3D model is only free to download if the owner enables it.
You can tell if a model is available for download if you see Download 3D Model below the viewer on the model page (like in the image below).
If the Download 3D Model link is not visible, the user has decided not to make their model downloadable.
Clicking Download 3D Model will offer the following:
- the original file that the author uploaded, along with any texture, material, and extra files that were included
- the transcoded glTF version of the model