  BICEP3, the latest telescope in the BICEP/Keck program, started science
observations in March 2016. It is a 550mm aperture refractive telescope
observing the polarization of the cosmic microwave background at 95 GHz. We
show the focal plane design and detector performance, including spectral
response, optical efficiency and preliminary sensitivity of the upgraded
BICEP3. We demonstrate 9.72$\mu$K$\sqrt{\textrm{s}}$ noise performance of the
BICEP3 receiver.
