We present Hubble Space Telescope (HST) photometry of 17 Cepheids in open clusters and their cluster mean parallaxes from Gaia EDR3. These parallaxes are more precise than those from individual Cepheids (
G< 8 mag) previously used to measure the Hubble constant because they are derived from an average of >300 stars per cluster. Cluster parallaxes also have smaller systematic uncertainty because their stars lie in the range ( G> 13 mag) where the Gaia parallax calibration is the most comprehensive. Cepheid photometry employed in the periodluminosity relation was measured using the same HST instrument (WFC3) and filters (F555W, F814W, F160W) as extragalactic Cepheids in Type Ia supernova hosts. We find no evidence of residual parallax offset in this magnitude range, zp= 3 4 as, consistent with the results from Lindegren et al. and most studies. The Cepheid luminosity (at P= 10 d and solar metallicity) in the HST near-infrared, Wesenheit magnitude system derived from the cluster sample is H0 = 72.9 1.3 and H0 = 73.3 1.1 km s1 Mpc1 with or without offset marginalization; combined with all other anchors we find H0 = 73.01 0.99 and 73.15 0.97 km s1 Mpc1, respectively, a 5% or 7% reduction in the uncertainty in H0 and a 5.3 Hubble tension relative to Planck+CDM. It appears increasingly difficult to reconcile two of the best-measured cosmic scales, parallaxes from Gaia and the angular size of the acoustic scale of the cosmic microwave background, using the simplest form of CDM to connect the two.