STIX MEM_GE non-thermal imaging results over the spectral range 32 – 76 keV during the rise phase of the SOL2024-05-20T05:14L171C109 (estimated-X16.5) flare. Left column: 32 – 76 keV integrated lightcurves. Grey regions show the 4 s interval imaged in each row. The red region shows the 1 s time bin encompassing the attenuator motion, during which images were not produced. Middle 4 columns: 1 s-integration images progressing in time from left to right, and then downward through each row. White/black lines show 40% and 80% contours relative to the peak intensity in each image. The colour table is scaled to be consistent across all 1 s images. The number of counts used for each image is given in the top right corner of each frame. Right column: 4 s-integration images corresponding to the same interval as the 1 s images in the same row. The contours and count labels are as in the middle rows, but the colour table is scaled across all 4 s images, and is not consistent with the 1 s images. Note that some rows show morphological changes on ≤1 s timescales that are not captured by the 4 s images.