We present deep Ks band Gemini GeMS/GSAOI observations of Westerlund 1, the most massive young Galacticstar cluster known. The high spatial resolution combined with a relatively stable point spread function across alarge eld of view provide unique possibilities to resolve the low-mass content of the cluster. We show that theclean point spread function is crucial in handling the source detection in this crowded eld suering extremelyhigh contrast from the brightest hypergiants in the cluster to faint brown dwarfs.