The continuous-time quantum walk on the 4.8.8 (truncated square) tiling exhibits a bifurcated operator-spreading light cone with two distinct group velocities, vfast = 0.81 and vslow = 0.60 shortest-path hops per unit time. The empirical velocity ratio (1.35) agrees to within 5% with the ratio of maximum group-velocity gradients extracted from the analytically diagonalised 4 × 4 Bloch Hamiltonian (1.42), the residual being consistent with an Airy wavepacket-centroid correction. Using a site-averaged out-of-time-order correlator (OTOC) echo protocol on N = 3600 nodes, we compare against a coordination-matched honeycomb lattice (z = 3) and a generic square lattice (z = 4); both controls produce single-velocity light cones, while the 4.8.8 wavefront cleanly bifurcates. A tertiary echo dip at t = 16 survives the N = 3600 scale-up, at which point the geometric boundary lies∼ 45 hops from the origin, confirming its bulk character; we attribute it to octagon-mediated recurrence. We interpret the result as a lattice-geometric analogue of optical birefringence, arising from the two inequivalent edge environments in the isogonal (vertex-transitive) 4.8.8 tiling rather than from any directional anisotropy. 2026-06-20 legacy canon revision: This is a canon-reconciled legacy version. Photon/relativity status changed via Gauss-projected and null-chain layers The paper retains its historical derivation trail but carries a 2026-06-20 canon revision note identifying current status and superseded claims. 2026-06-21 canon refresh: This version incorporates the 2026-06-21 ANCHOR/DRIFT/PTMS canon refresh and rebuilt local PDF.
David Elliman (Sun,) studied this question.