Introduction: Deucravacitinib, an oral, selective, allosteric TYK2 inhibitor, was superior to placebo and apremilast in two global, phase 3 trials (POETYK PSO-1 and PSO-2) in moderate to severe plaque psoriasis. At Week 52, patients could enter the POETYK long-term extension (LTE) trial and receive open-label deucravacitinib. Long-term efficacy was maintained through 3 total years of continuous treatment with no new safety signals in the ongoing LTE. Methods: Efficacy was further evaluated through Week 208 (4 years; data cutoff, November 1, 2023) in patients from the pooled PSO-1/PSO-2 populations who received continuous deucravacitinib from Day 1, achieved ≥75% reduction from baseline in Psoriasis Area and Severity Index (PASI 75) at Week 16 (primary endpoint) or Week 24 (peak response), and entered the LTE. Maintenance of response assessments included PASI 75, PASI 90, and sPGA 0/1 (static Physician Global Assessment score of 0 [clear]/1 [almost clear]). Efficacy is reported using modified nonresponder imputation in patients who reached or discontinued before Week 208. Results: Of 513 patients who received continuous deucravacitinib from Day 1 and entered the LTE, PASI 75 was achieved by 313 (61.0%) and 336 (65.5%) patients at Week 16 and Week 24. Among Week 16 PASI 75 responders, response rates were maintained well from Week 16 to Week 208 (PASI 75: 100%, 84.4%; PASI 90: 55.7%, 57.4%; sPGA 0/1: 82.8%, 65.4%). Among Week 24 PASI 75 responders, response rates were also maintained from Week 24 to Week 208 (PASI 75: 100%, 84.6%; PASI 90: 62.7%, 58.2%; sPGA 0/1: 82.5%, 66.0%). Conclusion: Clinical efficacy was generally maintained with continuous deucravacitinib in the vast majority of Week 16 and Week 24 PASI 75 responders from the parent trials through 4 years, supporting the long-term effectiveness and treatment durability of once-daily oral deucravacitinib for moderate to severe plaque psoriasis.