• Age \>= 18 years

• Eastern Cooperative Oncology Group (ECOG) performance status 0, 1, 2

• Histologically or cytologically confirmed diagnosis of multiple myeloma (MM), as defined in International Myeloma Working Group (IMWG) criteria, and:

‣ If patients have undergone stem cell transplantation (SCT), day 0 of SCT must be \> 100 days prior to registration to be eligible for the study

⁃ Has had disease progression after \>= 3 prior lines of anti-myeloma treatments including one proteasome inhibitor (eg. bortezomib, carfilzomib or ixazomib), one immunomodulatory agent (eg.thalidomide, lenalidomide or pomalidomide) and one anti-CD38 monoclonal antibody (eg.daratumumab or isatuximab)

⁃ Prior non-belantamab mafodotin anti-BCMA agent exposure is allowed; patients with prior treatment with an anti-BCMA chimeric antigen receptor (CAR)-T or bispecific antibody will be allowed to participate in the study

• Has measurable disease with at least one of the following:

‣ Serum M-protein \>= 0.5 g/dL (\>= 5 g/L)

⁃ Urine M-protein \>= 200 mg/24 h

⁃ Serum free light chain (FLC) assay: Involved FLC level \>= 10 mg/dL (\>= 100 mg/L) and an abnormal serum free light chain ratio (\< 0.26 or \> 1.65)

⁃ Note: Patients with non-secretory disease will be allowed to participate

• Absolute neutrophil count \>= 0.75 x 10\^9/L (=\< 28 days prior to registration)

‣ Without growth factor support, blood transfusion, or platelet stimulating agents for the past 14 days, excluding erythropoietin

• Hemoglobin \>= 7.0 g/dL (=\< 28 days prior to registration)

‣ Without growth factor support, blood transfusion, or platelet stimulating agents for the past 14 days, excluding erythropoietin

• Platelets \>= 50 x 10\^9/L (=\< 28 days prior to registration)

‣ Without growth factor support, blood transfusion, or platelet stimulating agents for the past 14 days, excluding erythropoietin

• Total bilirubin =\< 2.0 x upper limit of normal (ULN) (=\< 28 days prior to registration); (total bilirubin \>= 2.0 x ULN is acceptable if bilirubin is fractionated and direct bilirubin is \< 35%)

• Alanine aminotransferase =\< 2.5 x ULN (=\< 28 days prior to registration)

• Aspartate transaminase =\< 2.5 x ULN (=\< 28 days prior to registration)

• Estimated glomerular filtration rate (eGFR) \>= 30 mL/min/1.73 m\^2 (=\< 28 days prior to registration)

‣ As calculated by Modification of Diet in Renal Disease (MDRD) formula

• Spot urine \[albumin/creatinine ratios (spot urine)\] =\< 500 mg/g (56 mg/mmol) OR urine dipstick negative/trace \[if \>1+ only eligible if confirmed =\< 500 mg/g (56 mg/mmol) by albumin/creatinine ratio (spot urine from first void)\] (=\< 28 days prior to registration)

• Negative pregnancy test done =\< 7 days prior to registration, for persons of childbearing potential only. Both females and males must agree to follow the instructions

‣ NOTE: If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required

• Provide written informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the study protocol

• Willingness to provide mandatory blood specimens for correlative research

• Willing to return to enrolling institution for follow-up (during the Active Monitoring Phase of the study)