It included following changes: - Increased the target enrollment number from 200 to 250 to account for potential dropouts; - Clarified IBD nonresponders as those with a decrease in pMCS of < 2 points or an increase in pMCS; - After the Week 13 visit, IBD nonresponders discontinued study drug and commenced OL filgotinib 200 mg once daily; and at Week 26, if they did not have a ≥ 50% decrease in sperm concentration from baseline, had the option to continue receiving OL filgotinib as part of the LTE; - Any participants who demonstrated a ≥ 50% decrease in sperm concentration from baseline entered the MP regardless of when it occurred; - Clarified that participants would be allowed on conventional immunomodulators as defined by the inclusion criteria; - LTE defined as Week 26 to Week 221; - Updated the 30-day follow-up visit and the posttreatment visit to a safety follow-up visit; - Added a required safety follow-up visit 30 days after last dose of study drug at the end of the LTE and after an ET visit; - Clarified the inclusion criteria for tumor necrosis factor alpha (TNFα) antagonists; - Clarified for participants at screening who were taking allowed therapies for UC that they had to remain on stable doses for the noted times; - Excluded ustekinumab 12 weeks prior to screening; - Updated the inclusion criteria to require that semen volume be ≥ 1.5 mL, total sperm per ejaculate to be ≥ 39 M, and that participants be up to date on colorectal cancer surveillance as per local guidelines prior to screening; - Updated participants meeting the disease worsening criteria to be offered the option to commence OL filgotinib; - End of study defined as when the last participant completed the Week 225 visit or the last participant completed their last visit, whichever was sooner; - Updated study visit windows to ± 5 days for the primary study and ± 10 days during the LTE.

It included following changes: - Revised study title from UC to IBD to encompass CD; - Increased the number of study centers from approximately 150 centers to approximately 175 centers worldwide; - Broadened the age range from 25 to 55 years of age (inclusive) to 21 to 65 years of age (inclusive); - Included ≥ 50% decrease in sperm total motility and/or sperm morphology as decision criteria for participants to enter the MP; - Removed Week 28 and Week 32 visits from LTE; - Amended the definition of evaluable participants; - Added the option of pooling the results of this study with a separate study being conducted in participants with rheumatic diseases (Study GLPG0634-CL-227 [2018-003933-14]) with the same objective, and having the total planned number of participants in both studies combined of up to approximately 250 participants.

It included following changes: - Updated ejaculation-free period from ≥ 48 hours and < 5 days to ≥ 48 hours and ≤ 7 days, per the recommendation of the updated Food and Drug Administration (FDA) guidance for industry on testicular toxicity studies; - Clarified OL Week 13 study visit and visit schedule of LTE; - Amended lower threshold of baseline sperm concentration for inclusion (≥ 10 million sperm cells/mL changed to ≥ 15 million sperm cells/mL) in line with FDA recommendation, and amended corresponding sperm concentration randomization strata (lower range of stratum changed from 10 to 20 million sperm cells/mL to 15 to 25 million sperm cells/mL); - Added the option for an unblinded interim analyses when 200 participants (eg, pooled data from Studies GS-US-418-4279 and GLPG0634-CL-227) and/or when some defined subset(s) of participants had completed their Week 13 assessments.

It included following changes: - Included discontinuation criteria for thromboembolic events; - Included a criterion to trigger an ad-hoc data monitoring committee (DMC) meeting; - Clarified that the CDAI score calculation excluded days that involved an endoscopy procedure or preparation for that procedure; - Added section on blinding procedures.