The main purpose of this study is to evaluate the long-term efficacy of mirikizumab in pediatric participants with ulcerative colitis (UC) or Crohn's disease (CD). The study will last about 172 weeks and may include up to 44 visits. Additional treatment may be available to participants via a Continued Access Period.

Inclusion Criteria:

• Participants from originating studies (I6T-MC-AMBA [NCT05784246], I6T-MC-AMBU [NCT04004611], I6T-MC-AMAM [NCT03926130]) , I6T-MC-AMAY [NCT05509777]) who would, in the opinion of the investigator, derive clinical benefit from further treatment with mirikizumab
• Participants from prior studies who have completed assessments and procedures at last visit of originating study and remain on study drug treatment.
• Female participants must agree to contraception requirements.

Exclusion Criteria:

• Participants must not have developed a serious adverse event (SAE) or Adverse Event (AE) in originating study or developed other condition before first visit of Study AMAZ that continued treatment with mirikizumab would present an unreasonable risk for the participant.
• Participants must not have had permanently or temporarily stopped study drug in the originating study, such that restarting mirikizumab would pose an unacceptable risk for the participant in Study AMAZ.
• Participants must not have an unstable or uncontrolled illness that would potentially affect participant safety.
• Participants must not be enrolled in the study if, for any reason, being in the study would compromise the participant's safety or confound data interpretation.
• Participants must not have adenomatous polyps that have not been removed.
• Participants must not be pregnant or breastfeeding.

Anonymized individual patient level data will be provided in a secure access environment upon approval of a research proposal and a signed data sharing agreement.

Data are available 6 months after the primary publication and approval of the indication studied in the US and European Union (EU), whichever is later. Data will be indefinitely available for requesting.

A research proposal must be approved by an independent review panel and researchers must sign a data sharing agreement.