Compatibility of Drinfeld presentations and $q$-characters for affine Kac-Moody quantum symmetric pairs: quasi-split case

Let $(\mathbf{U},{\mathbf{U}}^{\mathrm{ı}})$ be a quasi-split affine quantum symmetric pair of type $\mathsf{A}\mathsf{I}\mathsf{I}\mathsf{I}$. This case is of particular interest thanks to the existence of geometric realizations and Schur–Weyl dualities. We establish factorization and coproduct formulae for the Drinfeld–Cartan series ${\mathbf{\Theta }}_i(z)$ in the Lu–Pan–Wang–Zhang `new Drinfeld’-style presentation, generalizing the split type results from [Prz23, LP25a]. As an application, we construct a boundary analogue of the $q$-character map, and show that it is compatible with Frenkel and Reshetikhin’s original $q$-character homomorphism.