  We present NuSTAR observations of the luminous neutron star low-mass X-ray
binary (NS LMXB) and Z source GX 5-1. During our three observations made with
separations of roughly two days, the source traced out an almost complete Z
track. We extract spectra from the various branches and fit them with a
continuum model that has been successfully applied to other Z sources.
Surprisingly, and unlike most of the (luminous) NS-LMXBs observed with NuSTAR,
we do not find evidence for reflection features in any of the spectra of GX
5-1. We discuss several possible explanations for the absence of reflection
features. Based on a comparison with other accreting neutron star systems and
given the high luminosity of GX 5-1 (~1.6-2.3 times the Eddington luminosity,
for a distance of 9 kpc), we consider a highly ionized disk the most likely
explanation for the absence of reflection features in GX 5-1.
