Earth's inner core exhibits strong seismic anisotropy, often attributed to the alignment of hexagonal close‐packed iron (hcp‐Fe) alloy crystallites with the Earth's poles. How this alignment developed depends on material properties of the alloy and is important to our understanding of the core's crystallization history and active geodynamical forcing. Previous studies suggested that hcp‐Fe is weak under deep Earth conditions but did not investigate the effects of the lighter elements known to be part of the inner core alloy. Here, we present results from radial X‐ray diffraction experiments in a diamond anvil cell that constrain the strength and deformation properties of iron‐nickel‐silicon (Fe–Ni–Si) alloys up to 60 GPa. We also show the results of laser heating to 1650 K to evaluate the effect of temperature. Observed alloy textures suggest different relative activities of the various hcp deformation mechanisms compared to pure Fe, but these textures could still account for the theorized polar alignment. Fe–Ni–Si alloys are mechanically stronger than Fe and Fe–Ni; extrapolated to inner core conditions, Si‐bearing alloys may be more than an order of magnitude stronger. This enhanced strength proportionally reduces the effectivity of dislocation creep as a deformation mechanism, which may suggest that texture developed during crystallization rather than as the result of postsolidification plastic flow. Plain Language Summary: The inner core is a Moon‐sized ball of solid metal at the very center of the Earth. Vibrations from earthquakes move faster through the inner core if they travel parallel to Earth's axis (the line between the North and South Poles) than if they travel parallel to the Equator. This probably means that the grains of metal in the inner core are themselves aligned with Earth's axis. Previous studies determined that this alignment likely happened after the inner core had formed, but those experiments were done on pure iron, whereas the inner core is mostly iron but also contains other elements. We did experiments at high pressures and temperatures on a more realistic core metal containing iron, nickel, and silicon. We found that this metal would be much stronger than pure iron at inner core pressures and temperatures; it is still possible for it to produce a north‐south alignment, but it is much more difficult for it to do so. This could mean that the alignment occurred while the inner core was forming (rather than afterward), which might change how we think about the forces present in the deep Earth today. Key Points: The inner core's seismic anisotropy can be explained by crystallographic alignment of a hexagonal close‐packed iron‐rich alloySample textures suggest that silicon‐bearing alloy deformation may be dominated by pyramidal and basal slip at low and high T, respectivelySilicon‐bearing alloys are stronger (harder to deform) at inner core conditions than pure iron and iron–nickel alloys [ABSTRACT FROM AUTHOR]