Subleading soft factor for string disk amplitudes

We investigate the behavior of superstring disk scattering amplitudes in the presence of a soft external momentum at finite string tension. We prove that there are no α′-corrections to the field theory form of the subleading soft factor S (1). At the end of this work, we also comment on the possibility to find the corresponding subleading soft factors in closed string theory using our result and the KLT relations.