Octagonal Steiner Minimal Trees (OSMTs) are used in the global routing phase of pervasive octagonal VLSI layout. The OSMT problem seeks a minimal length spanning structure using edges composed of line segments having one of four equally spaced orientations. The concept of a canonical form is introduced providing a strong framework for the structure and characteristics of OSMTs. An exact algorithm and a variety of pruning techniques are introduced. Random and OR Library instances are solved and compared against rectilinear and Euclidean SMTs. These experiments demonstrate the utility of pervasive octagonal routing, showing that octagonal SMTs are consistently 10% smaller than rectilinear SMTs. Categories and Subject Descriptors F.2.2 [Nonnumerical Algorithms and Problems]: Geometrical problems and computations; J.6 [Computer-Aided Engineering]: Computer-aided design General Terms Algorithms, Design, Theory Keywords Steiner Trees, Octagonal, Routing, Computer-Aided Design