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Abstract: This paper considers the effective degree of freedom (EDoF) for extremely large-scale multiple-inputmultiple-output (XL-MIMO) systems. We consider two XL-MIMO hardware designs: uniform planar array (UPA)based and continuous aperture (CAP)-based XL-MIMO as well as two representative near-field channel models: scalar Green’s function-based and dyadic Green’s function with triple polarization-based near-field channels. First, for UPA-based XL-MIMO a discrete array aperture, we evaluate the EDoF performance by applying discrete channel matrices generated by the scalar or dyadic Green’s channel model. Then, for CAP-based XL-MIMO, a tailored EDoF performance evaluation framework for a two-dimensional (2D) CAP plane-based system is constructed by leveraging asymptotic analysis and extending the analysis approaches for a one-dimensional (1D) CAP line segment-based system. This framework incorporates the triple polarized auto-correlation kernel function, which can efficiently capture the impact of multiple polarization on the EDoF performance. Numerical results show that, with an increase in the number of antennas, the UPA-based XL-MIMO system can achieve an EDoF performance close to the EDoF performance for the CAP plane-based XL-MIMO system. Moreover, the EDoF performance can be enhanced by the multiple polarization in channels and increased physical sizes of the transceiver.