Bulk samples with the chemical composition of the AIST phase-change material Ag3.4In3.7Sb76.4Te16.5 were synthesized by melt spinning as well as under high-pressure conditions (12 GPa), respectively. Rietveld refinements as well as selected-area electron diffraction patterns and high-resolution transmission electron images show that both types of samples crystallize in the gray As structure type. All atoms are disordered on one Wyckoff position. The metrics of the high-pressure sample appear compressed along  compared to the ones of the melt-spun sample. This may be attributed to strain, probably caused by twinning, which relaxes at higher temperatures (starting at ca. 130 °C). The compounds decompose at 250 °C and a structural change of the Sb-rich Sb/Te phase was observed at 440 °C. The thermoelectric properties of an annealed sample with AgInTe2 impurities were measured and result in a ZT value of 0.003 at room temperature, which strongly increases with temperature.