On the Theoretical Understanding of Inclusive $\Lambda_b$ Decays

I discuss a QCD sum rule determination of the four-quark operator matrix elements contributing to the $\Lambda_b$ inclusive decay rates at the order $m_b^{-3}$. The results suggest that $1/m_b^3$ corrections are not responsible of the observed difference between the lifetimes of $\Lambda_b$ and $B_d$.