In early 2025, the JHU-led Cosmology Large Angular Scale Surveyor (CLASS) project announced a first-of-its-kind measurement of the so-called “optical depth to reionization,” the probability that a photon from the cosmic microwave background interacts with electrons freed from intergalactic gas by starlight. Recently the US National Science Foundation awarded CLASS funding to improve this measurement, which is critical for interpreting the next generation of cosmological observations.