In‐plane distortion of a fiducial array was used as a metric to compare the relative responses to heat treatments of x‐ray masks doped with different brightener levels. Samples plated from gold‐sulfite baths containing 0, 2, and 75 ppm Tl all distorted by more than 50 nm after annealing at 100 °C. Quenching in liquid nitrogen fully relieved the stress of the undoped sample only. Room temperature stress relaxation behavior after storage of the gold samples for 2.5 years is detailed. Gold samples doped to any level with a thallium‐based brightener gradually relax, if initially stressed, and remain at a zero stress state. Behavior is explained in terms of room temperature grain growth and plastic deformation.