A Study to Evaluate the Long Term Safety and Efficacy of Bimekizumab in Subjects With Ankylosing Spondylitis

Inclusion Criteria:

- In the opinion of the Investigator, the subject is expected to benefit from
participation in an Open Label Extension (OLE) study

- Subject completed AS0008 without meeting any withdrawal criteria

- Female subjects must be postmenopausal, permanently sterilized or, if of childbearing
potential, must be willing to use a highly effective method of contraception

- Male subjects with a partner of childbearing potential must be willing to use a condom
when sexually active

Exclusion Criteria:

- Female subjects who plan to become pregnant during the study or within 20 weeks
following the last dose of investigational medicinal product (IMP). Male subjects who
are planning a partner pregnancy during the study or within 20 weeks following the
last dose

- Subjects with any current sign or symptom that may indicate a medically significant
active infection (except for the common cold) or has had an infection requiring
systemic antibiotics within 2 weeks of study entry

- Subjects who meet any withdrawal criteria in AS0008. For any subject with an ongoing
Serious Adverse Event, or a history of serious infections (including hospitalizations)
in the lead-in study, the Medical Monitor must be consulted prior to the subject's
entry into AS0009