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Abstract In this work, we publish stellar velocity dispersions, sizes, and dynamical masses for eight ultramassive galaxies (UMGs; $\log \left(M_{*}/M_{\odot }\right)$> 11),z≳ 3) from the Massive Ancient Galaxies Atz> 3 NEar-infrared (MAGAZ3NE) Survey, more than doubling the number of such galaxies with velocity dispersion measurements at this epoch. Using the deep Keck/MOSFIRE and Keck/NIRES spectroscopy of these objects in theHandKbandpasses, we obtain large velocity dispersions of ∼400 km s⁻¹for most of the objects, which are some of the highest stellar velocity dispersions measured and ∼40% larger than those measured for galaxies of similar mass atz∼ 1.7. The sizes of these objects are also smaller by a factor of 1.5–3 compared to this samez∼ 1.7 sample. We combine these large velocity dispersions and small sizes to obtain dynamical masses. The dynamical masses are similar to the stellar masses of these galaxies, consistent with a Chabrier initial mass function (IMF). Considered alongside previous studies of massive quiescent galaxies across 0.2 <z< 4.0, there is evidence for an evolution in the relation between the dynamical mass–stellar mass ratio and velocity dispersion as a function of redshift. This implies an IMF with fewer low-mass stars (e.g., Chabrier IMF) for massive quiescent galaxies at higher redshifts in conflict with the bottom-heavy IMF (e.g., Salpeter IMF) found in their likelyz∼ 0 descendants, though a number of alternative explanations such as a different dynamical structure or significant rotation are not ruled out. Similar to data at lower redshifts, we see evidence for an increase of IMF normalization with velocity dispersion, though thez≳ 3 trend is steeper than that forz∼ 0.2 early-type galaxies and offset to lower dynamical-to-stellar mass ratios.