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This study demonstrates that we can break the strength-ductility paradox in face-centered cubic (FCC) high-entropy alloys (HEAs) by introducing local chemical ordering. Employing high-resolution transmission electron microscopy, atom probe tomography, and electron-chanelling contrast imaging in CoFeNi and CoCrFeNi HEAs with (Al/Ti) additions, we report a planar-slip-induced strain-hardening mechanism that operates at significantly higher stresses compared to the well-known transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) mechanisms. Our results provide clear evidence that the introduction of chemical ordering in HEAs promotes localized slip along multiple {111} planes. Importantly, the interactions between planar slip activities on non-parallel {111} planes triggers a dynamic Hall-Petch like effect that continually refines the slip length. This is in contrast to hexagonal closed …