Robust spectroscopic redshifts from the first half of RUBIES PRISM observations (obtained January–March 2024). Left: Comparison between the best-fit photometric redshifts used for target selection versus the best-fit spectroscopic redshift (z_prism). Middle: Spectroscopic redshift distribution for all targets and the subset of red targets, defined as F150W−F444W>2. Dashed lines show the median redshifts. Right: Differences between the photometric and spectroscopic redshifts. Overall, there is good agreement between the photometric and spectroscopic redshifts. However, for red sources, the photometric redshift scatter is a factor of three higher than for the census sample, with an outlier fraction that is a factor of three higher than for similarly bright sources that are less red. This illustrates the need for spectroscopy, particularly for red sources.