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The environments where galaxies reside play a key role in shaping their star formation histories over cosmic time, yet such environmental effects remain elusive at high redshifts. We update this environmental process by adopting an advanced measure for cluster in-fall time using kinematics and reveal that galaxies experience a gradual decline of star formation after they fall into cluster environments up to $z \sim 1$. This conclusion is drawn from a uniform analysis of a remarkably large sample of 105 clusters and 1626 spectroscopically-confirmed member galaxies from the SPT and ACT Sunyaev-Zel'dovich surveys at 0.26 $< z, Comment: 21 pages, 9 figures, 3 tables. Submitted to ApJ. Posted after referee report; comments very welcome

The environments where galaxies reside play a key role in shaping their star formation histories over cosmic time, yet such environmental effects remain elusive at high redshifts. We update this environmental process by adopting an advanced measure for cluster in-fall time using kinematics and reveal that galaxies experience a gradual decline of star formation after they fall into cluster environments up to $z \sim 1$. This conclusion is drawn from a uniform analysis of a remarkably large sample of 105 clusters and 1626 spectroscopically-confirmed member galaxies from the SPT and ACT Sunyaev-Zel'dovich surveys at 0.26 $< z, 21 pages, 9 figures, 3 tables. Submitted to ApJ. Posted after referee report; comments very welcome

We present and publicly release (https://www.gclasshst.com) the first spatially resolved H$��$ maps of star-forming cluster galaxies at $z\sim1$, made possible with the Wide Field Camera 3 (WFC3) G141 grism on the Hubble Space Telescope (HST). Using a similar but updated method to 3D-HST in the field environment, we stack the H$��$ maps in bins of stellar mass, measure the half-light radius of the H$��$ distribution and compare it to the stellar continuum. The ratio of the H$��$ to stellar continuum half-light radius, $R[\mathrm{H}��/\mathrm{C}]=\frac{R_{\mathrm{eff, H}��}}{R_{\mathrm{eff, Cont}}}$, is smaller in the clusters by $(6\pm9)\%$, but statistically consistent within $1��$ uncertainties. A negligible difference in $R[\mathrm{H}��/\mathrm{C}]$ with environment is surprising, given the higher quenched fractions in the clusters relative to the field. We postulate that the combination of high quenched fractions and no change in $R[\mathrm{H}��/\mathrm{C}]$ with environment can be reconciled if environmental quenching proceeds rapidly. We investigate this hypothesis by performing similar analysis on the spectroscopically-confirmed recently quenched cluster galaxies. 87% have H$��$ detections, with star formation rates $8\pm1$ times lower than star-forming cluster galaxies of similar stellar mass. Importantly, these galaxies have a $R[\mathrm{H}��/\mathrm{C}]$ that is $(81\pm8)\%$ smaller than coeval star-forming field galaxies at fixed stellar mass. This suggests the environmental quenching process occurred outside-in. We conclude that disk truncation due to ram-pressure stripping is occurring in cluster galaxies at $z\sim1$, but more rapidly and/or efficiently than in $z\lesssim0.5$ clusters, such that the effects on $R[\mathrm{H}��/\mathrm{C}]$ become observable just after the cluster galaxy has recently quenched., 21 pages, 7 figures, Accepted for publication in ApJ