Non-formality conjecture for the algebras $E_m^n$

Let $E_m^n$ denote the Ext algebra considered in the paper, equipped with its induced algebra structure and viewed as a differential graded algebra up to quasi-isomorphism. Non-formality conjecture. In general, the algebra $E_m^n$ is not formal. This conjecture asserts that the non-vanishing higher multiplications found in particular minimal models cannot always be eliminated by replacing the model; establishing non-formality requires showing that an appropriate higher multiplication defines a nontrivial Hochschild-cohomology class. The general question remains open in the source.