Locally isotropic Steinberg groups II. Schur multipliers

We compute Schur multipliers of locally isotropic Steinberg groups and of all root graded Steinberg groups with root systems of rank at least $3$ (excluding the types ${\mathsf{H}}_3$ and ${\mathsf{H}}_4$). As an application, we show that locally isotropic Steinberg groups are well defined as abstract groups.