ABY-029 will be administered at the 6X dose level prior to surgery to participants with presumed high-grade glioma, based on a preoperative MRI or other imaging. Investigators will collect one blood sample before participants are given ABY-029, a second sample one or two minutes after participants are given the drug, a third sample about 15 minutes after participants are given the drug, and a fourth sample about an hour after receiving the drug, or just prior to anesthesia (whichever comes first). Investigators will collect one urine sample and take EKG readings to monitor the participant's heart before surgery. Investigators will repeat blood, urine and EKG tests when participants are in the hospital after surgery.

ABY-029 will be administered at the 10X dose level prior to surgery to participants with presumed high-grade glioma, based on a preoperative MRI or other imaging. Investigators will collect one blood sample before participants are given ABY-029, a second sample one or two minutes after participants are given the drug, a third sample about 15 minutes after participants are given the drug, and a fourth sample about an hour after receiving the drug, or just prior to anesthesia (whichever comes first). Investigators will collect one urine sample and take EKG readings to monitor the participant's heart before surgery. Investigators will repeat blood, urine and EKG tests when participants are in the hospital after surgery.

ABY-029 will be administered via single intravenous injection to subjects with high-grade glioma approximately 1-3 hours prior to surgery.

All research procedures will occur during surgery. The research procedures involve image and measurement data collection and biopsy specimen sampling. Research data collection will occur at 3 or 4 time points during surgery using either standard-of-care tools and methods or non-significant risk experimental devices.

No follow-up visit will be required of participants. Participants will be monitored for possible adverse events for approximately 30 days by the operating surgeon involved in the clinical trial procedures and through review of participant medical records.

To study the safety of ABY-029, adverse events related to 6X and 10X doses of ABY-029 will be tracked following surgery, and the proportion of study-drug related adverse events at 6X and 10X doses will be compared statistically for significant differences.

To measure of diagnostic performance of ABY-029, the false negative rate of ABY-029 fluorescence measured during surgery in tissue samples that are confirmed to be tumor through pathology.