In the title compound, C(17)H(17)N(3)O(2)S, the phenyl ring is oriented at dihedral angles of 8.5 (2) and 1.17 (14)°, respectively, to the C=N-N plane and the fused aromatic ring. The thia-zine ring adopts an envelope conformation with the S atom at the flap. In the crystal, a weak C-H⋯O inter-action connects the mol-ecules, forming a helical chain along the a axis.