Homogeneous Algebraic Varieties and Transitivity Degree

Let $X$ be an algebraic variety such that the group $\mathrm {Aut}(X)$ acts on $X$ transitively. We define the transitivity degree of $X$ as the maximum number $m$ such that the action of $\mathrm {Aut}(X)$ on $X$ is $m$-transitive. If the action of $\mathrm {Aut}(X)$ is $m$-transitive for all $m$, the transitivity degree is infinite. We compute the transitivity degree for all quasi-affine toric varieties and for many homogeneous spaces of algebraic groups. We also discuss a conjecture and open questions related to this invariant.