As of today, all underground stations now are equipped with free public wifi. Metro just announced the milestone, which is the culmination of a pilot program that began in 2016. The goal is to expand free wifi to all of Metro’s aboveground stations, so that all 91 Metrorail stations will have wifi by the end of 2018. Work is also underway currently to provide full cell service in all tunnel segments.
To log in at an underground station, just select “Metro-Public” network from your phone or device’s Wi-Fi settings.