This study is a randomized, double-blind, placebo-controlled trial in which eligible IPF subjects will be randomized to receive GBT440 or Placebo orally daily.

Inclusion Criteria:

• Documented diagnosis of IPF.
• Oxygen desaturation with exercise.
• Completion of the baseline 6MWT
• Weight ≥ 50 kg
• Male or female of child bearing potential willing and able to use highly effective methods of contraception from study start to 3 months after the last dose of study drug.

Exclusion Criteria:

• FEV1/FVC < 70%.
• Subjects on supplemental oxygen therapy at rest.
• History of other interstitial lung diseases.
• Significant polycythemia.
• Female who is breast-feeding or pregnant.
• Known current malignancy or history of malignancy within the last 2 years prior to screening.
• Use of cytotoxic and/or immunosuppressant medications within 30 days screening.
• Hospitalization due to an exacerbation of IPF within 30 days of screening
• Subject plans to begin or has commenced pulmonary rehabilitation within 30 days of screening
• Corticosteroids (> 10 mg per day of prednisone or an equivalent) within 30 days of screening.
• Current smoker or history of smoking within 3 months of screening.
• Currently or, in the opinion of the investigator, soon to be listed for lung transplant.
• History of unstable or deteriorating cardiac or pulmonary disease (other than IPF) within 6 months of screening.
• Any condition possibly affecting drug absorption.
• Participated in another clinical trial of an investigational drug (or medical device) within 30 days or 5-half-lives, whichever is longer, prior to screening, or is currently participating in another trial of an investigational drug (or medical device).
• Subject who, for any reason, is deemed by the investigator to be inappropriate for this study.