The news: they skipped the vanadium. It's ferrocyanide / ferrogluconate based.

But whoever mentioned the 6000 cycle figure should kindly quote their source, because I can't find it.

Herein, we propose a highly stable alkaline all-iron flow battery for LDES by pairing the [Fe(CN)6]3−/[Fe(CN)6]4− redox couple with the ferric/ferrous-gluconate (Gluc−) complexes redox couple, which exhibits high solubility (1.2 mol L−1), fast redox kinetics and high stability in alkaline media. The high stability of iron-gluconate complexes resulted from the stable six-coordinated iron species, enabling a stable alkaline all-iron flow battery, which can stably run for 950 cycles at a current density of 80 mA cm−2.