In a chemostat with a dilution rate of $0.8$ $h^{-1}$, the steady state biomass concentration and the specific product formation rate are $8 \textit{ mol m}^{-3}$ and $0.2 \;(\textit{mol product}) (\textit{mol biomass})^{-1} \: h^{-1}$, respectively. The steady state product concentration in $\textit{mol m}^{-3}$ is ___________