There will be two additional southbound trips from Westlake Station, at 12:58 a.m. and 1:13 a.m. The last northbound trip isn’t so late—it leaves Sea-Tac Station at 12:20 a.m.
On Sunday, New Year’s Day, and also on Monday, January 2, Link will run on a Sunday schedule, which means that the first northbound train won’t reach Beacon Hill Station until 6:43 a.m., and trains will run only every 10 minutes during most of the day. Service will return to normal on Tuesday, January 3.