The cosmic microwave background (CMB) serves as a unique backlight for tracing the growth of cosmic structures. By measuring arc-minute-scale deflections experienced by CMB photons due to gravitational lensing, we can map matter distributions at high redshifts. This lensing signal provides a powerful probe of fundamental physics—such as the sum of neutrino masses—and enables consistency tests of the standard cosmological model by comparing observed and predicted large-scale structure growth.
In this talk, I will review recent and forthcoming advances in this rapidly evolving field, with a particular focus on the DR6 CMB lensing results from the Atacama Cosmology Telescope (ACT). I will also discuss ongoing efforts to produce state-of-the-art lensing maps using the final data release of ACT by combining night-time, daytime, and large-scale CMB observations from Planck. I will then explore the transformative potential of the Simons Observatory and discuss the implications of these lensing measurements in the context of understanding cosmic structure growth and addressing the S₈ tension.