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Based on cascaded Mach-Zehnder interferometer (MZI) lattice filters, we demonstrate and compare silicon O-band 8-channel (de-)multiplexers with flat and Gaussian-like passbands for the 400 GBASE-LR8 norm. The 1×8 (de-)multiplexer with flat passbands exhibit insertion loss less than 2.5 dB, channel crosstalk lower than −11 dB, and 3 dB bandwidths of ∼3.9 nm. In contrast, the maximum insertion loss, the worst channel crosstalk, and 3 dB bandwidths of the 1×8 (de-)multiplexer with Gaussian-like passbands are 1.1 dB, −13 dB, and ∼2.9 nm, respectively. The comparison result indicates that the latter is more advisable choice. A theoretical calculation based on measured coupling ratios of stand-along directional couplers (DC) indicates that the performance deteriorations of practical filtering curves are mainly caused by dispersions and fabrication errors of the DCs.