Inclusion Criteria:
1. Male or female ≥18 years of age.
2. Histologic diagnosis of GIST with co-occurring KIT exons 11+17/18 mutations confirmed by ctDNA sample.
3. Participants must have advanced GIST and radiologic progression on imatinib treatment.
4. Eastern Cooperative Oncology Group (ECOG) performance status (PS) of ≤2 at screening.
5. Female participants of childbearing potential must have a negative pregnancy test at screening and prior to the first dose of study drug.
6. Participants of reproductive potential must agree to follow contraception requirements.
7. Participants must have at least 1 measurable lesion according to mRECIST v1.1 within 21 days prior to the first dose of study drug.
8. Adequate organ function and bone marrow reserve based on laboratory assessments performed at screening.
9. Resolution of all toxicities from prior therapy to Grade ≤1 (or participant baseline) within 1 week prior to the first dose of study drug.

Exclusion Criteria:
1. History of KIT exon 9 mutation or detection of KIT exon 9, 13, or 14 mutations in a ctDNA sample.
2. Has known active central nervous system metastases.
3. New York Heart Association Class II-IV heart disease, myocardial infarction within 6 months of Cycle 1 Day 1, active ischemia or any other uncontrolled cardiac condition such as angina pectoris, clinically significant cardiac arrhythmia requiring therapy, uncontrolled hypertension, or congestive heart failure.
4. Use of strong or moderate inhibitors or inducers of cytochrome P450 (CYP) 3A prior to the first dose of study drug, and consumption of grapefruit or grapefruit juice within 14 days prior to the first dose of study drug.
5. Major surgeries (eg, abdominal laparotomy) within 4 weeks of the first dose of study drug.
6. Known human immunodeficiency virus or hepatitis C infection only if the participant is taking medications that are excluded per protocol, acute or chronic hepatitis B, or acute or chronic hepatitis C infection.
7. Gastrointestinal abnormalities including, but not limited to:
1. inability to take oral medication
2. malabsorption syndromes
3. requirement for intravenous alimentation
8. Any active bleeding excluding hemorrhoidal or gum bleeding.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 5/3/2024. Questions regarding updates should be directed to the study team contact.