The basic unit of this model is an octahedron made from a single sheet of "silver rectangle" shape that I created five years ago. In 2017 I had the idea to use the octahedron model to achieve this fractal after being inspired by a photograph of a similar model by Dave Mitchell I saw on the internet.
Strictly speaking, the Sierpinski 3D fractal is not a modular origami model, because the octahedra are not joined together but simply sit on top of each other. The octahedra are then arranged and placed side by side in a pyramidal shape (Tetrahedron), halving the format of the starting sheet gradually and then the edge of the octahedron. The result is a nice fractal of Sierpinski 3D. Depending on the number of octahedra of different dimensions used, the name is identified with level 1, level 2, level 3, etc.
Click on photo for diagrams.