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We present spectroscopic confirmation of five galaxy clusters at $1.25 <\textit{z} < 1.5$, discovered in the $2500$ deg$^{2}$ South Pole TelescopeSunyaev-Zel'dovich (SPT-SZ) survey. These clusters, taken from a mass-limitedsample with a nearly redshift independent selection function, havemulti-wavelength follow-up imaging data from the X-ray to near-infrared, andcurrently form the most homogeneous massive high-redshift cluster sample known.We identify $44$ member galaxies, along with $25$ field galaxies, among thefive clusters, and describe the full set of observations and data products fromMagellan/LDSS3 multi-object spectroscopy of these cluster fields. We brieflydescribe the analysis pipeline, and present ensemble analyses of cluster membergalaxies that demonstrate the reliability of the measured redshifts. We report$\textit{z} = 1.259, 1.288, 1.316, 1.401$ and $1.474$ for the five clustersfrom a combination of absorption-line (Ca II H$\&$K doublet - $3968,3934${\AA}) and emission-line ([OII] $3727,3729$ {\AA}) spectral features. Moreover,the calculated velocity dispersions yield dynamical cluster masses in goodagreement with SZ masses for these clusters. We discuss the velocity andspatial distributions of passive and [OII]-emitting galaxies in these clusters,showing that they are consistent with velocity segregation and biases observedin lower redshift SPT clusters. We identify modest [OII] emission andpronounced CN and H$\delta$ absorption in a stacked spectrum of $28$ passivegalaxies with Ca II H$\&$K-derived redshifts. This work increases the number ofspectroscopically-confirmed SZ-selected galaxy clusters at $\textit{z} > 1.25$from three to eight, further demonstrating the efficacy of SZ selection for thehighest redshift massive clusters, and enabling detailed study of thesesystems.

Spectroscopic Confirmation of Five Galaxy Clusters at z > 1.25 in the 2500 sq. deg. SPT-SZ Survey