Yes, riders can now add a SmarTrip card to iPhone and Apple Watch, and simply hold their device near the card reader to pay anywhere SmarTrip is accepted: all 91 Metrorail stations in DC, Maryland and Virginia; all Metro parking garages and lots; all Metrobus routes; and all regional bus providers, including ART, DASH, Fairfax Connector, Cue, Ride On, The Bus, Circulator, Loudoun County Transit, and Potomac and Rappahannock Transit/PRTC.
SmarTrip on iPhone and Apple Watch provides riders a "touch-free" experience and a safer way to pay. Riders do not need to touch card readers or vending machines, and with Express Transit, they can move quickly through stations and fare gates without the need to use Face ID, Touch ID, or wake their device.
For more information view news release:
https://www.wmata.com/about/news/SmarTrip-now-available-on-iPhone-and-Apple-Watch.cfm