This OLE study is designed to evaluate long-term safety, tolerability, and efficacy of filgotinib in patients with polyarticular or systemic juvenile idiopathic arthritis (pJIA-sJIA) who have completed the treatment period/prolonged treatment period of the parent studies and demonstrated clinical benefit defined as control of disease activity through improvement in signs and symptoms as per Investigator judgement.

Inclusion Criteria:

• Subject must have completed treatment with filgotinib in at least one parent study and achieved a clinical benefit at the end of the parent protocols
• Subject and/or parent/legal guardian must be able and willing to comply with the clinical study protocol requirements and must sign and date the informed consent form and assent (if required per local regulation) as approved by the Independent Ethics Committee/ Institutional Review Board, prior to any protocol evaluations
• Female or male subject 8 to <18 years of age, on the date of signing the informed consent and assent (per local regulation) form
• Female subject of childbearing potential who is sexually active and at risk for pregnancy must agree to use contraception/preventive exposure measures as described in the clinical study protocol.

Exclusion Criteria:

• Development of any condition during the parent study that would preclude safe continuation
• Pregnancy
• Active infection that is clinically significant, as per Investigator's judgement
• Subject with known hypersensitivity to the components of potential study therapy
• Subjects with any condition or circumstances (including abnormalities in laboratory parameters) that, in the opinion of the investigator, may make a subject unlikely or unable to complete the study or comply with study procedures and requirements