  We prove the existence of $\mathrm{GSpin}_{2n}$-valued Galois representations
corresponding to cohomological cuspidal automorphic representations of certain
quasi-split forms of $\mathrm{GSO}_{2n}$ under the local hypotheses that there
is a Steinberg component and that the archimedean parameters are regular for
the standard representation. This is based on the cohomology of Shimura
varieties of abelian type, of type $D^{\mathbb{H}}$, arising from forms of
$\mathrm{GSO}_{2n}$. As an application, under similar hypotheses, we compute
automorphic multiplicities, prove meromorphic continuation of (half) spin
$L$-functions, and improve on the construction of $\mathrm{SO}_{2n}$-valued
Galois representations by removing the outer automorphism ambiguity.
