On Wednesday, the friends and collaborators celebrated their big Grammy win during a night out at West Hollywood hotspot Maia, a source tells PEOPLE.
Swift, 26, made her grand arrival in an all-white pantsuit. With her double-breasted jacket open, the singer revealed her toned midriff, but true to form, her belly button was under wraps.
Once inside the restaurant, Swift and Antonoff, 31 – boyfriend of Swift's pal Lena Dunham – headed to the intimate dining room on the second level and feasted on tuna truffle pizza, yellowtail sashimi, halibut ceviche and lobster quesadillas, an onlooker says. As for Swift's cocktail of choice, the onlooker says she sipped on Maia's pink cadillac cocktail.
The stars have a lot to celebrate: Swift's album 1989 – for which Antonoff co-wrote and produced "Out of the Woods" and "I Wish You Would" – won album of the year at the Grammys this month. "The duo were overheard reminiscing about the early times of Taylor's career and how far she has come," the source says.
Swift and the Fun musician have also united in support of Kesha, who is fighting to record and release new music without producer Dr. Luke after accusing him of sexually, physically, verbally and emotionally abusing her.
While Swift donated $250,000 to help cover Kesha's financial needs, Antonoff offered to produce new music with Kesha.
Dunham, 29, also has Kesha's back. Earlier this week, the Girls star defended her in an emotional Lenny newsletter, writing in part, "When I saw the outcome of Kesha's court case last Friday, I felt sick."