Reflection gratings offer high dispersion and thus the potential for high spectral resolution in the soft x-ray band. The requirements of high efficiency and maximum collecting area at minimum mass lead to the desire for densely stacked and exquisitely flat thin-foil grating substrates. In the past we have successfully addressed the problems of thin substrate figure metrology and blazed grating profile fabrication. Our recently developed low-stress thin-foil metrology truss with 50 nm figure repeatability removed a metrology bottleneck and allows us to make progress in the shaping of thin-foil substrates. We present results on the figuring of 100 mm-diameter silicon wafers via magnetorheological finishing to a flatness below 100 nm peak-to-valley, allowing for sub-arcsecond reflection optics.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.