Large angular scale polarimetry of the CMB will provide powerful constraints on the cosmological parameters r, the tensor-to-scalar ratio, and tau, the optical depth to the epoch of reionization. The Cosmology Large Angular Scale Surveyor (CLASS) is targeting these scales by conducting a survey from the Atacama, covering ~75% of the sky, across four frequency bands straddling the foreground minimum.

The fast modulation technology enabling recovery of these scales also makes the instrument uniquely sensitive to circular polarization. Even with partial survey data, CLASS is able to place constraints on circularly polarized emission that are orders of magnitude better than previous limits. I will give an update on the CLASS survey and present first results on the circular polarization measurements at 40 GHz.