One of the famous "millennium prize problems" is the "Yang–Mills existence and mass gap" problem, which in its official description by E. Witten and A. Jaffe has the following form:
"Prove that for any compact simple gauge group $G$, a non-trivial quantum Yang–Mills theory exists on $\mathbb{R}^{4}$ and has a mass gap $∆>0$. Existence includes establishing axiomatic properties at least as strong as those cited in [Wightman, Streater: "PCT, Spin and Statistics, and All That"] and [Osterwalder, Schrader: "Axioms for Euclidean Green’s functions"]."
I would like to know about the current status of this problem. Since the official problem announcement around 2000, there have been many successes in mathematical QFT. I am not only talking about axiomatic and constructive field theory, but also about modern approaches, like algebraic QFT (and is generalizations, i.e. perturbative AQFT and locally covariant QFT) as well as in functorial (and topological) QFT. So what is the current status, especially with respect to all this recent mathematical developments?