GLB is the binary file format representation of 3D models saved in the GL transmission format (glTF). Information about 3D models such as node hierarchy, cameras, materials, animations and meshes in binary format. This binary format stores the glTF asset (JSON, .bin and images) in a binary blob. It also avoids the issue of increase in file size which happens in case of glTF. GLB file format results in compact file sizes, fast loading, complete 3D scene representation, and extensibility for further development. The format uses model/gltf-binary as MIME type.
FBX, FilmBox, is a popular 3D file format that was originally developed by Kaydara for MotionBuilder. It was acquired by Autodesk Inc in 2006 and is now one of the main 3D exchange formats as used by many 3D tools. FBX is available in both binary and ASCII file format. The format was established to provided interoperability between digital content creation applications.