Inflationary models generically predict that a gravitational-wave background (GWB) would have been produced along with the density perturbations that seed large-scale structure.

A measurement of B-mode polarization in the CMB would be important confirmation of inflation and would provide a rare glimpse into physics at ultra-high energies.

A better understanding of cosmic dawn will also help other experiments measure the sum of the masses of the three known neutrino types using the gravitational lensing of the CMB.

[10] Additional science goals for CLASS are to better understand our own Milky Way Galaxy and to search for evidence of exotic new physics through constraining circular polarization in the CMB and large-scale anomalies.

The CLASS instrument is designed to survey 65% of the sky at millimeter wavelengths, in the microwave portion of the electromagnetic spectrum, from a ground-based observatory with a resolution of about 1° — approximately twice the angular size of the sun and moon as viewed from Earth.

[11] To measure such a small signal, CLASS employs focal plane arrays with large numbers of feedhorn-coupled, transition-edge-sensor bolometers cooled to just 0.1 °C above absolute zero by cryogenic helium refrigerators.

This allows for a clear separation of the tiny polarization of the CMB from the much larger unpolarized atmosphere by "locking in" to the 10 Hz signal.

Because water vapor in the atmosphere emits at microwave frequencies, CLASS observes from a very dry and high-altitude site in the Andes Mountains on the edge of the Atacama Desert of Chile.

The CLASS 40 GHz telescope achieved first light on 8 May 2016 and began a roughly five-year survey in September 2016 after initial commissioning observations were complete.