In this paper, we present a soft x-ray variable line-spacing spherical grating monochromator, which is shared between the three ATHOS beamlines at SwissFEL. The instrument uses grazing incidence angles of less than 3° to withstand the peak-fluence of femtosecond FEL pulses with energies up to 8 mJ. The upward facing monochromator grating facilitates endstations with different beam heights. We explain the integration of the monochromator into the beamlines; discuss its mechanical design, its control system and its optical components. We conclude with showing an initial calibration spectrum and detail the currently achieved performance.