Constraining Inflation with the BICEP/Keck Program

The BICEP/Keck (BK) program operates a series of small-aperture polarization-sensitive experiments measuring the cosmic microwave background (CMB). The program focuses on the "B-mode" polarization of the CMB, which at large angular scales are directly sourced by primordial gravitational waves. The strength of the B-mode signature is parameterized by the tensor-to-scalar r and measures the energy scale of cosmic inflation. The BK program has led the field in setting constraints on r (most recently, sigma(r)=0.009) and continues to improve its dataset with continued operation of BICEP3 and the deployment of the BICEP Array, which installed its high-frequency receiver during the 2024-2025 austral summer. In this talk, we give a brief overview of the BK program, highlight progress on fully instrumenting the BICEP Array receivers, discuss improvements to the analysis pipeline, and preview the path to a sensitivity of sigma(r)<0.003 with data through the 2027 observing season.