Rachel Rampy (Keck) Near-infrared tip/tilt sensing at Keck: System architecture and on-sky performance The sky coverage and performance of laser guide star (LGS) adaptive optics (AO) systems is limited by the natural guide star (NGS) used for low order correction. This limitation can be reduced by measuring image motion of the NGS in the near-infrared where it is partially corrected by the LGS AO system and where stars are generally several magnitudes brighter than at visible wavelengths. We have integrated a near-infrared tip-tilt sensor with the Keck I telescope's LGS AO system and recently began offering it for science use. The implementation involved modifications to the AO bench, real-time control system, higher level controls and operations software. The tip-tilt sensor is a H2RG-based near-infrared camera with 0.05 arc second pixels. Low noise at high sample rates is achieved by only reading a small region of interest, from 2x2 to 16x16 pixels, centered on an NGS anywhere in the 100 arc second diameter field. The sensor operates at either Ks or H-band using light reflected by a choice of dichroic beam-splitters located in front of the OSIRIS integral field spectrograph. I will present an overview of the completed system along with on-sky performance results. Lessons learned and efforts to extend the capabilities and further optimize the system are also discussed.