This open-label extension study will evaluate the long-term safety, tolerability and efficacy of orally inhaled seralutinib in subjects who have completed a previous seralutinib study

The treatment period is planned to run until the market approval of seralutinib or until the study is terminated.

Inclusion Criteria:

1. Subjects must have completed a qualifying last visit in a prior seralutinib PAH study on investigational product (IP) and in accordance with the protocol.
2. Evidence of an informed consent document, signed and dated by the subject, indicating that the subject has been informed of all pertinent aspects of the study prior to initiation of any subject-mandated procedures.
3. Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures
4. Women of childbearing potential (WOCBP) must have a negative urine or serum pregnancy test at enrollment visit before first administration of Investigational Product (IP) in this study.
5. WOCBP who are not abstinent and intend to be sexually active with a non-sterilized male partner must be willing to use a highly effective method of contraception from consent through 30 days following the last administration of IP.
6. Male subjects: Non-sterilized male subjects who are not abstinent and intend to be sexually active with a female partner of childbearing potential must use a male condom from consent through 90 days after the last dose of IP.

Exclusion Criteria:

1. Severe acute or chronic medical or laboratory abnormality that may increase the risk associated with study participation or seralutinib administration, unless associated with an ongoing AE and discussed with the Sponsor's medical monitor (MM) (or designee).
2. Have any other condition or reason that, in the opinion of the Investigator, would prohibit the subject from participating in the study.