The primary objective of this study is to observe the long-term safety of filgotinib in adults who have completed or met protocol specified efficacy discontinuation criteria in a prior filgotinib treatment study in ulcerative colitis (UC).

Key Inclusion Criteria:

• Must have the ability to understand and sign a written informed consent form (ICF), which must be obtained prior to initiation of study procedures associated with this trial
• Must have enrolled in Gilead-sponsored UC parent protocol GS US 418-3898 or any other Gilead/Galapagos-sponsored filgotinib treatment study for UC
• Must have completed all required procedures or met protocol-specified efficacy discontinuation criteria in a prior filgotinib treatment study for UC
• Females of childbearing potential must have a negative pregnancy test at Day 1
• Female individuals of childbearing potential who engage in heterosexual intercourse must agree to use protocol specified method(s) of contraception for the duration described
• Willingness to refrain from live or attenuated vaccines during the study and for 12 weeks after last dose of study drug

Key Exclusion Criteria:

• Known hypersensitivity to the study drug
• Any chronic medical condition (including, but not limited to, cardiac or pulmonary disease, alcohol or drug abuse) that, in the opinion of the Investigator or sponsor, would make the subject unsuitable for the study or would prevent compliance with the study protocol
• Females of reproductive potential who are unwilling to abide by protocol-specified contraceptive methods as defined
• Use of prohibited medications as outlined in the protocol

NOTE: Other protocol defined Inclusion/ Exclusion criteria may apply.

Only 3 arms are blinded in this study.