Comparing Rubin-GC1 (gold star) to the predicted stellar debris from the Sagittarius dSph (blue) in the simulations from E. Vasiliev et al. (2021). (Top Left) Galactocentric Y versus X. (Top Center) Z versus X. (Top Right) Z versus Y. To guide the eye, we overplot the rough extent of the Galactic disk (gray rectangle) and the position of the Sun (⊙) and Galactic Center (+). (Bottom Left) Proper motion in R.A. (μ_α*) versus R.A. (Bottom Center) Proper motion in decl. (μ_δ) versus decl.. (Bottom Right) Line-of-sight velocity versus Galactocentric radius. We find good agreement between the available 5D phase-space properties of Rubin-GC1 and the Sagittarius debris, and we predict that Rubin-GC1 will have the highest probability of association with Sagittarius if its mean radial velocity is measured to be v_hel ≈ 100–200 km s⁻¹.