The Cosmology Large Angular Scale Surveyor (CLASS) is uniquely built to probe the largest angular scales in the cosmic microwave background (CMB) polarization from its high site in Chile’s Atacama Desert. It has already produced polarization maps of 75% of the sky. This award supports observations and data analysis to develop instrumentation, observing strategies, and analysis techniques to understand and reduce systematic errors while increasing the sensitivity of the surveyor. Along with a substantially improved estimate of the reionization optical depth, the continuing survey will be able to access the unique imprint of inflationary gravitational waves in the CMB B-mode polarization. The CLASS faculty and postdocs work with Baltimore science teachers to increase public awareness of science and foster scientific interests in school-age children. CMB cosmology-focused educational resources developed will integrate into the Next Generation Science Standards in Maryland and other states. The project continues to train the next generation, having involved some 55 undergraduates and 20 graduate students, and provided leadership training for postdocs. The survey will provide stringent constraints on the redshift of cosmic dawn, of particular interest as new high-redshift galaxy populations are uncovered by the James Webb Space Telescope. The optical depth measurement is also critical for neutrino mass constraints. The survey will test exotic physics, including large-sc