In the present work we address the Thermodynamic Bethe Ansatz and ground state energy of the AdS3 × S3 × T4 model from the associated mirror superstring model in the pure RR background. Independently, we show complete consistency with wrapping interaction formalism and derive generalised Lüscher expression for GSE. We prove that the underlying mirror Y-system becomes solvable in various parametric regimes of the lightcone superstring theory. Moreover the contribution of the gapless worldsheet modes coming from the T4 can be computed exactly. Next we implement the lightcone AdS3 × S3 × T4 superstring sigma model with twisted boundary conditions on the fields. It then allows us to find the ground state energy in the semi-classical approximation, where string tension h and lightcone momentum L are infinite and the ratio is fixed. Comparison of semi-classical results demonstrates that there is a full agreement with the computation from AdS3 TBA. We also emphasize the massless factor discrepancy with respect to the initial conjecture arXiv:2112.08898 and show that it is related to the Y-functions describing massless excitations. We also make a mixed flux proposal from the TBA and find complete correspondence with our computation from the AdS3 × S3 × S3 × S1 lightcone superstring.