Artin's conjecture that the maximal abelian extension of the rationals is $C_1$

Let $\mathbf{Q}^{\mathrm{ab}}$ denote the maximal abelian extension of the rational numbers. Artin's conjecture. The field $\mathbf{Q}^{\mathrm{ab}}$ is $(C_1)$. The source presents this as an open problem for number fields and gives no resolution of this assertion.