The purpose of this study is to evaluate how well IBI3003 works when compared with the investigator's choice regimen (DPd or PVd)

This study is an open, multicenter, randomized controlled phase III clinical trial aimed at evaluating the efficacy and safety of IBI3003 compared to the investigator's choice regimen (DPd or PVd) in participants with relapsed or refractory multiple myeloma who have previously received 1-4 lines of therapy and have been exposed to three classes of drugs (proteasome inhibitors, immunomodulators, and anti-CD38 monoclonal antibodies). The plan is to enroll approximately 255 participants, who will be randomly assigned to the experimental group and the control group in a 2:1 ratio. Approximately 170 participants in the experimental group will receive IBI3003 treatment, while about 85 participants in the control group will receive the investigator's choice of treatment (DPd or PVd). Participants in the experimental group can discontinue medication for observation after meeting the criteria for stopping treatment. During the discontinuation period, if they meet the re-treatment criteria, following discussion between the investigator and the sponsor, and based on the participant's preference, IBI3003 re-treatment may be given until the criteria for terminating treatment are met.

Inclusion Criteria：

1. Age ≥18 years.

2. Documented initial diagnosis of multiple myeloma according to IMWG diagnostic criteria.

3. At least one of the following measurable disease indicators:

   • Serum M-protein ≥ 5 g/L（For IgA and IgD subtypes, it is recommended to use quantitative immunoglobulin measurements instead of M protein）
   • Urine M-protein ≥200 mg/24h
   • Serum free light chain (FLC) test: affected FLC level ≥100 mg/L and abnormal serum FLC ratio (<0.26 or >1.65)

4. Life expectancy ≥3 months.

5. Fertile females and sexually active fertile males must agree to use highly effective contraception (failure rate <1% per year) during the study and for 90 days after the last dose of the investigational drug. For participants in the clinical trial, contraceptive measures must comply with local regulations regarding the use of contraceptive methods. Females and males must agree not to donate eggs (ova, oocytes) or sperm during the study and for 90 days after the last dose of the investigational drug.

6. Willing and able to comply with the prohibitions and restrictions specified in this protocol.

Exclusion Criteria：

1. Previous treatment with any BCMA-targeted therapy and any GPRC5D-targeted therapy. Patients who have received either BCMA-targeted or GPRC5D-targeted therapy are allowed to participate in the study.
2. Known active CNS involvement or exhibits clinical signs of meningeal involvement of multiple myeloma.
3. Spinal cord compression that leads to limited self-care ability occurs within six months prior to informed consent or is expected to occur in the near future.
4. Have history of primary immunodeficiency.
5. Have history of organ transplantation.
6. Have received allogeneic hematopoietic stem cell transplantation within 6 months before the first administration of the study drug, or have received autologous stem cell transplantation within 3 months before the first administration of the study drug.