In this work we propose an energy-efficient, implantable, real-time, blind Adaptive Stimulation Artifact Rejection (ASAR) engine. This enables concurrent neural stimulation and recording for state-of-the-art closed-loop neuromodulation systems. Two engines, implemented in 40nm CMOS, achieve convergence of <;42μs for Spike ASAR and <;167μs for LFP ASAR, and can attenuate artifacts up to 100mV p-p by 49.2dB, without any prior knowledge of the stimulation pulse. The LFP and Spike ASAR designs occupy an area of 0.197mm 2 and 0.209mm 2 , and consume 1.73μW and 3.02μW, respectively at 0.644V.