Layers > Sculpt using layers >
Combine all layers onto the base level

Flatten combines all layers and applies the sculpting information to the original base level for the mesh and then deletes the layers.

1. In the Layers window, ensure the display button is set to Sculpt.
2. In the Layers window, do either of the following:
   - From the Layers window menu ( ), select Flatten.
   - Right-click in the Layers window and select Flatten from the menu that appears.