• Patient must be ≥ 18 years of age at the time of signing the informed consent form (ICF).

• Patient must have histologically confirmed recurrent or progressive WHO Grade 2 glioma or Grade 3 glioma with IDH1 R132H or R132C mutation confirmed by immunohistochemistry or molecular genetic testing.

⁃ 4\. The IDH mutation, and other applicable gene/molecular alterations (see Table 10-2) are determined by a validated assay as performed in Clinical Laboratory Improvement Amendments (CLIA)-certified/College of American Pathologists (CAP)-accredited or locally equivalent clinical laboratories. Prior clinical pathology report fulfilling the diagnosis criteria prior to screening with tumor samples collected is acceptable for patient enrollment in both Part 1 and Part 2.

⁃ 5\. Patient has received no more than 2 prior therapies for disease recurrence/progression.

⁃ 6\. Patient has disease recurrence or progression or cannot tolerate the most recent therapy.

⁃ 7\. Patient must have a measurable lesion(s) as per the RANO-HGG criteria for primarily enhancing lesions or RANO-LGG criteria for primarily non-enhancing lesions. The lesion (s) must be visible on 2 or more axial slices and have perpendicular diameters of at least 10 × 10 mm. The definition of primarily enhancing lesions or primarily non-enhancing lesions is referred to Section 8.3.1.

• Must be ≥18 years old at the time of signing the ICF.

• Diagnosis of histologically confirmed IDH1-mutant Grade 3 with high risk features or Grade 4 astrocytoma, per WHO 2021 classification and Investigator Assessment.

• Have an IDH1 mutation (R132H/C/G/S/L) based on IHC (R132H only), polymerase chain reaction (PCR), or next-generation sequencing (NGS). CDKN2A/B status and at least 1 of the following must be confirmed: absence of 1p19q co-deletion by fluorescence in situ hybridization, array comparative genomic hybridization, or NGS; presence of an ATRX loss of function mutation by NGS; or loss of normal ATRX expression by IHC. A validated assay performed in a CLIA-certified/CAP-accredited (or local equivalent) clinical laboratory must be used for all of the aforementioned results. Documentation of biomarker status, including redacted molecular pathology and NGS reports, must be provided during Screening.

• Must not have experienced disease recurrence or disease progression.

• Participants must have completed radiation therapy with a minimum of 90% of planned treatment completed (with or without concurrent temozolomide) and between 6 and 12 cycles of adjuvant temozolomide and have no evidence of disease progression. Randomization must occur at least 28 days and not more than 75 days after the final dose of temozolomide.

• Must agree to submit sufficient tumor tissue for retrospective biomarker and histological analyses. This requirement may be waived in rare circumstances with approval by the Sponsor.

• Has adequate hematologic and organ functions