An Adaptive Program of IKT-001 in Pulmonary Arterial Hypertension (PAH)

Inclusion Criteria: * Documented diagnosis of WHO PAH Group 1 in any of the following subtypes: * Idiopathic PAH * Heritable PAH * Drug/toxin-induced PAH * PAH associated with connective tissue disease (CTD) * PAH associated with simple, congenital systemic-to-pulmonary shunts at least 1 year following repair * Men and women 18 and 75 years of age (inclusive) * Must have a body mass index (BMI) of ≥18.5 kg/m\^2 and ≤35.0 kg/m\^2 at screening. * Baseline RHC performed during the Screening Period documenting a PVR of ≥ 400 dyn/sec/cm\^5 ; pulmonary capillary wedge pressure (PCWP) ≤15 mmHg and mean pulmonary artery pressure (mPAP) \>20 mmHg. PVR enrichment criteria to ensure population baseline PVR \>700 dynes/sec/cm\^5 * On stable doses of background PAH therapy including endothelin receptor antagonists, phosphodiesterase-5 inhibitors, prostacyclins, and soluble guanylate cyclase stimulators for ≥90 days prior to screening. Current use of sotatercept is not permitted. * 6MWD ≥ 100 and ≤ 475 m Exclusion Criteria: * Diagnosis of PAH WHO Groups 2, 3, 4, or 5. * Diagnosis of the following PAH Group 1 subtypes: human immunodeficiency virus (HIV)-associated PAH, PAH associated with portal hypertension, schistosomiasis-associated PAH, and pulmonary veno-occlusive disease. * Any of the following blood pressure-related values or abnormalities: Uncontrolled systemic hypertension as evidenced by sitting systolic BP \>160 mmHg or sitting diastolic BP \>100 mmHg at screening, Baseline systolic BP \<90 mmHg at screening, Syncope within 3 months prior to screening * History of restrictive, constrictive, or congestive cardiomyopathy. * ECG with Fridericia's corrected QT interval (QTcF) ≥ 450 msec in males or ≥ 470 msec in females at screening or ≥500 msec in the presence of a right bundle branch block. * Personal or family history of long QT syndrome or sudden cardiac death. * Presence of a CardioMEMS device or any other implanted hemodynamic monitoring device. * Forced vital capacity (FVC) \<70 percent on pulmonary function test (PFT) performed no more than 6 months prior to screening; or if FVC is 60 percent to 69 percent, must have a chest computed tomography scan within 12 months with no more than mild interstitial lung disease. * History of atrial fibrillation or atrial flutter. * History of cerebrovascular accident, intracranial hemorrhage, or subdural hematoma at anytime, or a fall associated with head trauma within 3 months of screening. * Acutely decompensated right heart failure within 30 days prior to screening, as per investigator assessment. * Clinically significant ischemic, valvular, constrictive heart disease, or heart failure with preserved ejection fraction in the opinion of the investigator. * History of pneumonectomy. * Untreated or inadequately treated (in the opinion of the investigator) obstructive sleep apnea. * Acute or chronic hepatitis B or C infection, defined as: * Hepatitis B virus: a positive hepatitis B surface antigen test or a positive hepatitis B core antibody test with detectable DNA * Hepatitis C virus (HCV): a positive hepatitis C antibody test with detectable HCV ribonucleic acid (RNA).Participants with a positive hepatitis C antibody test, but no detectable HCV RNA who completed treatment with direct-acting antivirals may be considered after discussion with the medical monitor. * History of or currently diagnosed with a bleeding disorder, including but not limited to hemophilia, von Willebrand disease, thrombocytopenia, or significant bleeding history defined as any bleeding event requiring medical intervention. * Received treatment with any of the following excluded medications: * Currently receiving strong cytochrome P450 (CYP) 3A inducers or CYP3A inhibitors (except for topical administration) * Currently receiving or anticipated need to receive any anticoagulant (e.g., heparins, vitamin K antagonists, direct oral anticoagulants, or direct thrombin inhibitors). * Current use of sotatercept. Note: participants who previously received sotatercept may be considered if the last dose administered was \>6 months prior to screening, participant had no significant bleeding events while on sotatercept. * Initiation of an exercise program for cardiopulmonary rehabilitation within 90 days prior to screening or planned initiation during the study (participants who are stable in the maintenance phase of a program and who will continue for the duration of the study are eligible). * History of atrial septostomy within 180 days prior to screening. * Current participation in another investigational clinical trial and/or receipt of any investigational medication within 90 days prior to screening. * Previous randomization into this or another IKT-001 study. * Any social, behavioral, or medical reason that would preclude completion of the study, in the judgement of the investigator. * Currently lactating, pregnant or planning on becoming pregnant during the study. * Prior receipt of a solid organ transplant or stem cell transplant. * Planned surgery that would require any study drug interruption or interfere with study assessments during the study (minor procedures may be allowed in consultation with the medical monitor). * Malignancy within the last 5 years prior to consent except completely treated non-metastatic-basal cell, squamous cell, in situ cervical cancer, and clinically localized National Comprehensive Cancer Network very low to low risk prostate cancer under active surveillance.