Participants who were receiving icotrokinra in either induction studies 1 or 2 and were in response at Week 12 of the induction study will be randomized to receive icotrokinra maintenance dose 1. Participants receiving Icotrokinra Dose 1 and meeting criteria for loss of response during the Maintenance Study will be eligibile for a single blinded dose adjustment to Icotrokinra Dose 2. After completion of the Maintenance Study through Week 40, eligible participants can participate in long-term extension (LTE).

Participants who were receiving icotrokinra in either induction studies 1 or 2 and were in response at Week 12 of the induction study will be randomized to receive icotrokinra maintenance dose 2. Participants who were non-responders at Week 12 of the induction studies will also receive icotrokinra maintenance dose 2 but will not be randomized. After completion of the Maintenance Study through Week 40, eligible participants can participate in LTE.

Participants who were receiving icotrokinra in either induction studies 1 or 2 and were in response at Week 12 will be randomized to receive placebo. Participants receiving placebo in induction studies 1 or 2 and in response at Week 12 of the induction study will continue to receive placebo during maintenance on non-randomized basis. Placebo non-responders from induction study will receive icotrokinra maintenance dose 2 on a non-randomized basis and will be assessed for response at Week 12.

Participants receiving placebo and meeting criteria for loss of response during the Maintenance Study will be eligible for a single blinded dose adjustment to icotrokinra dose 2. After completion of the Maintenance Study through Week 40, eligible participants can participate in LTE.

Matching placebo will be administered orally, daily.

An AE is any untoward medical occurrence in a clinical study participant administered a pharmaceutical (investigational or non-investigational) product that does not necessarily have a causal relationship with the intervention. An SAE is any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, is a suspected transmission of any infectious agent via a medicinal product and is medically important.

PRO-2 remission is defined as an abdominal pain (AP) mean daily score less than or equal to (<=) 1 and stool frequency (SF) mean daily score <= 2.8, and no worsening of AP or SF from baseline.

Clinical response is defined as a >= 100-point reduction from baseline in CDAI score.

Clinical remission is defined as CDAI score < 150. Endoscopic response is defined as > 50% improvement from baseline in SES-CD score or a decrease of at least 2 points in participants with a baseline score of 4 and isolated ileal disease. This is a composite endpoint defined to measure achievement of both clinical remission and endoscopic response at the participant level.

Clinical response is defined as a >= 100-point reduction from baseline in CDAI score.

Endoscopic remission is defined as SES-CD <= 4 with at least a 2-point reduction from baseline and no sub score >1 in any individual component.

Deep remission is a composite endpoint defined as achieving both clinical remission and endoscopic remission at the participant level. Clinical remission is defined as CDAI score < 150-point. Endoscopic remission is defined as SES-CD <= 4 with at least a 2-point reduction from baseline and no sub score >1 in any individual component.

IBDQ remission is defined as IBDQ score >= 170. IBDQ is a validated, 32-item, self-reported questionnaire for participants with inflammatory bowel disease (IBD) that will be used to evaluate the disease-specific health-related quality of life (HRQoL) across 4 dimensional scores: bowel symptoms (loose stools, abdominal pain), systemic symptoms (fatigue, altered sleep pattern), social function (work attendance, need to cancel social events), and emotional function (anger, depression, irritability). Scores range from 32 to 224, with higher scores indicating better outcomes.

Fatigue response is defined as a >= 7 point reduction in the patient reported outcomes measurement information system (PROMIS)-Fatigue Short Form 7a total score from baseline. The PROMIS fatigue SF-7a contains 7 items evaluating fatigue-related symptoms (that is, tiredness, exhaustion, mental tiredness, and lack of energy) and associated impacts on daily activities (that is, activity limitations related to work, self-care, and exercise). Item responses are rated on a five-point scale ranging from "never" to "always". Higher scores indicate more fatigue.

Clinical remission is defined as CDAI score< 150.

Histologic remission is defined as a Robarts Histopathology Index score <=3, where each of the items of lamina propria neutrophils, neutrophils in epithelium, and erosions or ulcerations must be equal to 0. Endoscopic remission is defined as SES-CD <= 4 with at least a 2-point reduction from baseline and no sub score >1 in any individual component. This is a composite endpoint defined as achieving both histologic remission and endoscopic remission at the participant level.

An AE is any untoward medical occurrence in a clinical study participant administered a pharmaceutical (investigational or non-investigational) product that does not necessarily have a causal relationship with the intervention. An SAE is any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, is a suspected transmission of any infectious agent via a medicinal product and is medically important.

PRO-2 remission is defined as an abdominal pain (AP) mean daily score <= 1 and stool frequency (SF) mean daily score <= 2.8, and no worsening of AP or SF from baseline.

Endoscopic remission is defined as SES-CD <= 4 with at least a 2-point reduction from baseline and no sub score >1 in any individual component.

90-day corticosteroid-free clinical remission is defined as the clinical remission at the visit and not receiving corticosteroids for at least 90 days prior to the visit. Clinical remission is defined as CDAI score < 150.

Participants with clinical remission at Week 40 among those with clinical remission at Week 0 of the maintenance study will be analyzed. Clinical remission is defined as CDAI score < 150.

Clinical remission is defined as CDAI score < 150. Endoscopic response is defined as > 50% improvement from baseline in SES-CD score or a decrease of at least 2 points in participants with a baseline score of 4 and isolated ileal disease. This is a composite endpoint defined to measure achievement of both clinical remission and endoscopic response at the participant level.

Deep remission is a composite endpoint defined as achieving both clinical remission and endoscopic remission at the participant level. Clinical remission is defined as CDAI score < 150. Endoscopic remission is defined as SES-CD <= 4 with at least a 2-point reduction from baseline and no sub score >1 in any individual component.

Histologic remission is defined as a Robarts Histopathology Index score <=3, where each of the items of lamina propria neutrophils, neutrophils in epithelium, and erosions or ulcerations must be equal to 0. Endoscopic remission is defined as SES-CD <= 4 with at least a 2-point reduction from baseline and no sub score >1 in any individual component. This is a composite endpoint defined as achieving both histologic remission and endoscopic remission at the participant level.

IBDQ remission is defined as IBDQ score >= 170. IBDQ is a validated, 32-item, self-reported questionnaire for participants with IBD that will be used to evaluate the disease-specific HRQoL across 4 dimensional scores: bowel symptoms (loose stools, abdominal pain), systemic symptoms (fatigue, altered sleep pattern), social function (work attendance, need to cancel social events), and emotional function (anger, depression, irritability). Scores range from 32 to 224, with higher scores indicating better outcomes.

Fatigue response is defined as a >= 7 point reduction in the PROMIS-Fatigue Short Form 7a total score from baseline. The PROMIS fatigue SF-7a contains 7 items evaluating fatigue-related symptoms (that is, tiredness, exhaustion, mental tiredness, and lack of energy) and associated impacts on daily activities (that is, activity limitations related to work, self-care, and exercise). Item responses are rated on a five-point scale ranging from "never" to "always". Higher scores indicate more fatigue.

An AE is any untoward medical occurrence in a clinical study participant administered a pharmaceutical (investigational or non-investigational) product that does not necessarily have a causal relationship with the intervention. An SAE is any untoward medical occurrence that at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, is a suspected transmission of any infectious agent via a medicinal product and is medically important.