Rollout will be complete by Spring. Full list, per the TSA:

• Alaska Airlines: ATL, DCA, DEN, JFK, LAS, LAX, ORD, PDX, SEA, SFO, SLC
• American Airlines: ATL, CTL, DCA, DEN, DFW, EWR, IAD, IAH, JFK, LAS, LAX, LGA, MSP, ORD, PBI, PDX, PHL, SFO, SEA, SLC
• Delta Air Lines: ATL, DCA, DEN, DTW, EWR, JFK, LAS, LAX, LGA, ORD, PDX, SEA, SFO, SLC
• Southwest Airlines: ATL, DEN, LAX, LGA, ORD, PDX, SEA, SFO, SLC
• United Airlines: ATL, DCA, DEN, EWR, LAS, LAX, LGA, ORD, PDX, SEA, SFO, SLC

Alaska and American passengers with TSA PreCheck can participate, but unlike a KTN, you can’t just add this to a booking. You have to be a member of that airline’s loyalty program and opt in from your account settings (which means you can’t use this if you’re with Alaska and flying American, or vice versa, or you’re with another oneworld airline, flying either).