A Study of Xaluritamig Plus Abiraterone Versus Investigator's Choice in Participants With Chemotherapy-naïve Metastatic Castration-resistant Prostate Cancer

The primary objective of this study is to compare overall survival (OS) in participants receiving xaluritamig plus abiraterone against investigator's choice (docetaxel, cabazitaxel, or abiraterone).

Inclusion Criteria: * Participant has provided informed consent before initiation of any study-specific activities/procedures. * Age ≥ 18 years (or ≥ legal age within the country if it is older than 18 years) at the time of signing the informed consent. * Participant must have histological, pathological, and/or cytological confirmation of adenocarcinoma of the prostate. Mixed histologies (eg, adenocarcinoma with neuroendocrine component) are not permitted. * Metastatic castration-resistant prostate cancer (mCRPC) with ≥ 1 metastatic lesion that is present on baseline computed tomography (CT), magnetic resonance imaging (MRI), or bone scan imaging obtained within 28 days before enrollment. * Evidence of progressive disease (PD), defined as 1 or more PCWG3-modified RECIST 1.1 criteria: * Serum PSA progression is defined as 2 consecutive increases in PSA over a previous reference value measured at least 1 week prior. The minimum start value is 2.0 ng/mL. * Soft-tissue progression defined as an increase ≥ 20% in the sum of the diameter (SOD) (short axis for nodal lesions and long axis for non-nodal lesions) of all target lesions based on the smallest SOD since treatment started or the appearance of 1 or more new lesions or unequivocal progression of existing non-target lesions. * Progression of bone disease defined by the appearance of at least 2 new bone lesions(s) by bone scan (as per the 2+2 PCWG3-modified RECIST 1.1 criteria). * Participants must have had prior orchiectomy and/or ongoing androgen-deprivation therapy (ADT) and a castrate level of serum testosterone (\< 50 ng/dL or \< 1.7 nmol/L). * Prior disease progression on 1, and only 1, androgen receptor pathway inhibitor (ARPI) (either enzalutamide, apalutamide, or darolutamide) is required. * Participants intended to receive cabazitaxel must have previously received ≤ 6 cycles of docetaxel in the metastatic hormone-sensitive prostate cancer (mHSPC) setting. * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1. * Adequate organ function. Exclusion Criteria: Disease Related: * Participants with a history of central nervous system (CNS) metastases. * Unresolved toxicities from prior antitumor therapy not having resolved to CTCAE version 5.0 grade 1 or baseline, with the exception of alopecia or toxicities that are stable and well-controlled AND there is an agreement to allow inclusion by both the investigator and the sponsor. Prior/Concomitant Therapy: * Prior six transmembrane epithelial antigen of the prostate 1 (STEAP1)-targeted therapy. * Prior disease progression on or intolerance to abiraterone. * Prior treatment with any chemotherapy regimen in the mCRPC setting and/or \> 6 cycles of docetaxel treatment in the mHSPC setting. * Any anticancer therapy, immunotherapy, or investigational agent within 4 weeks before first dose of study treatment with the following exceptions: * Androgen receptor pathway inhibitors (ARPIs; enzalutamide, darolutamide, apalutamide): minimum washout of 2 weeks prior to the first dose of study treatment. * Androgen suppression therapy (eg, luteinizing hormone-releasing hormone/gonadotrophin releasing hormone \[LHRH/GnRH\] analogue \[agonist/antagonist\]) is permitted. * Prior radioligand therapy (RLT) within 8 weeks of first dose of study treatment. * Prior radionuclide therapy (radium-223) within 2 months of first dose of study treatment. * Prior palliative radiotherapy within 2 weeks before first dose of study treatment. Participants must have recovered from all radiation-related toxicities. * Concurrent cytotoxic chemotherapy, ARPI, immunotherapy, RLT, poly adenosine diphosphate ribose polymerase (PARP) inhibitor, biological therapy, investigational therapy. * Treatment with live and live-attenuated vaccines within 4 weeks before the first dose of study treatment. * Prior CD3-directed therapy.