The primary objective of this study is to demonstrate that KAI-9531 subcutaneous (SC) injection once weekly is superior to placebo on:

• Percent change in body weight
• Change in hemoglobin A1c (HbA1c)

Key Inclusion Criteria:

• Diagnosis of type 2 diabetes mellitus (T2DM).
• Receiving stable therapy for T2DM for 3 months prior to Screening. This includes diet/exercise alone and any oral medication for T2DM treatment except for glucagon-like peptide-1 receptor (GLP-1R) agonist, GLP-1R/glucose-dependent insulinotropic polypeptide receptor (GIPR) dual agonist, or dipeptidyl peptidase-4 (DPP-4) inhibitors.
• BMI ≥27 kg/m^2.
• History of at least 1 self-reported unsuccessful effort to lose weight with diet and exercise within the prior 6 months.

Key Exclusion Criteria:

• Current diagnosis or history of type 1 diabetes mellitus (T1DM) or any other type of diabetes except T2DM.
• History of diabetic ketoacidosis or hyperosmolar state/coma within 1 year prior to Screening.
• History of severe hypoglycemia or hypoglycemia unawareness within 1 year prior to Screening.
• Started medications within 3 months prior to Screening that may cause significant weight gain, including, but not limited to, tricyclic antidepressants, atypical antipsychotics, and mood stabilizers.
• Unstable weight defined as self-reported change in body weight exceeding 5% within 3 months prior to Screening.
• Family or personal history of multiple endocrine neoplasia Type 2 or medullary thyroid cancer.
• Uncontrolled hypertension or unstable cardiovascular disease.
• History of chronic or acute pancreatitis.
• Known clinically significant gastric emptying abnormality or chronic treatment with medications that directly affect gastrointestinal (GI) motility if taken for >30 days continually within 3 months prior to Screening.
• History of suicide attempt.
• History of significant active or unstable Major Depressive Disorder (MDD) or other severe psychiatric disorder within 2 years prior to Screening.
• Received treatment with semaglutide, tirzepatide, GLP-1 receptor agonists, GLP-1/glucose-dependent insulinotropic polypeptide (GIP) agonists, glucagon receptor agonists, or other weight loss medications or treatments aside from diet and exercise within 3 months prior to Screening.

Note: Additional inclusion/exclusion criteria may apply, per protocol.