A model-independent anatomy of $\Delta F= 2$ transitions in the context of the Weak Effective Theory (WET) below the electroweak scale (EW) and the Standard Model Effective Field Theory (SMEFT) above the EW scale is discussed. Two master formulae for the BSM contribution of the mixing amplitude $M_{12}$, in terms of Wilson coefficients are presented.
The coefficients entering these formulae contain all the information below the EW scale and the NP scale $\Lambda$, respectively. The renormalization group evolution from the top-quark Yukawa coupling has the largest impact on the result. The obtained expressions depend on whether the down-basis or the up-basis for SMEFT operators is considered.