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The tidal disruption of the Sagittarius dwarf galaxy has generated aspectacular stream of stars wrapping around the entire Galaxy. We use data from$Gaia$ and the H3 Stellar Spectroscopic Survey to identify 823 high-qualitySagittarius members based on their angular momenta. The H3 Survey is largelyunbiased in metallicity, and so our sample of Sagittarius members is similarlyunbiased. Stream stars span a wide range in [Fe/H] from $-0.2$ to $\approx-3.0$, with a mean overall metallicity of $\langle$[Fe/H]$\rangle=-0.99$. Weidentify a strong metallicity-dependence to the kinematics of the streammembers. At [Fe/H]$\gt -0.8$ nearly all members belong to the well-known cold($\sigma_v \lt 20$ km/s) leading and trailing arms. At intermediatemetallicities ($-1.9 \lt$[Fe/H]$\lt -0.8$) a significant population (24$\%$)emerges of stars that are kinematically offset from the cold arms. These starsalso appear to have hotter kinematics. At the lowest metallicities([Fe/H]$\lesssim-2$), the majority of stars (69$\%$) belong to thiskinematically-offset diffuse population. Comparison to simulations suggeststhat the diffuse component was stripped from the Sagittarius progenitor atearlier epochs, and therefore resided at larger radius on average, compared tothe colder metal-rich component. We speculate that this kinematically diffuse,low metallicity, population is the stellar halo of the Sagittarius progenitorsystem.

A Diffuse Metal-Poor Component of the Sagittarius Stream Revealed by the H3 Survey