We have observed the peculiar superluminal quasar 4C 39.25 with the ROSAT PSPC at two epochs. We examine both short‐term (constant flux on intraday and several‐day timescales) and long‐term (30% increase over 2 yr) variability of the soft X‐ray emission. The entire radio to submillimeter spectrum also rose by 30% over the same period. This supports the twisted relativistic jet model for 4C 39.25 (Marscheret al. 1991), in which the Doppler beaming factor increases monotonically as the velocity vector of the superluminally moving component (here identified as the source of the X‐rays) continues to bend toward the line of sight. ©1994 American Institute of Physics