In 2021, the dynamics of three-dimensional (extremal) black holes on General Relativity with negative cosmological constant were showed equivalent to two independent copies of the AKNS system. This duality was addressed through the imposition of suitable boundary conditions to the Chern-Simons action. In this scheme, the involution of conserved charges of the AKNS system yields an infinite-dimensional commuting asymptotic symmetry algebra of gravitational charges.