• Previously diagnosed with AL amyloidosis based on IMWG criteria who have relapsed or refractory disease after treatment with at least one prior line of therapy (minimum 2 cycles).

• Participants must have progression of light chain disease, defined as dFLC \>20mg/L.

• For Phase 2 only, measurable hematologic disease, satisfying one of the following criteria: Difference between involved and uninvolved free light chain (FLC) over 40 mg/L; Abnormal level of FLC with an abnormal κ/λ ratio (except in participants with CKD stage 3 or higher where a rise of lambda FLC to an abnormal level and of at least 50% over the nadir with a normal κ/λ ratio is acceptable); A serum M spike measuring ≥ 0.5 g/dL

• Age ≥ 18 years

• ECOG performance status ≤2 or Karnofsky ≥60%

• Participants must meet the following organ and marrow function as defined below: Absolute leukocyte count ≥3,000/mcL , Absolute neutrophil count ≥1,000/mcL, Absolute platelet count ≥75,000/mcL , Direct bilirubin ≤1.5 × institutional upper limit of normal (ULN) AST(SGOT)/ALT(SGPT) ≤3 × institutional ULN, Creatinine: Calculated clearance ≥30 mL/min using Cockcault-Groft equation

• Participants who received belantamab mafodotin are eligible if discontinued due to intolerance or adverse event.

• For participants with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated.

• Participants with a history of hepatitis C virus (HCV) infection must have been treated and cured. For participants with HCV infection who are currently on treatment, they are eligible if they have an undetectable HCV viral load.

• AL Amyloidosis Cardiac stage I, II or IIIa disease based on the 2013 European Modification of the 2004 Standard Mayo Clinic Staging in participants with advanced cardiac involvement (Dispenzieri et al., 2004; Wechalekar et al., 2013).

• The effects of elranatamab on the developing human fetus are unknown. Based on the mechanism of action, elranatamab may cause fetal harm when administered to a pregnant woman and therefore should not be used during pregnancy. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation and until 90 days since the last dose of elranatamab. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 90 days after completion of elranatamab administration.

• Ability to understand and the willingness to sign a written informed consent document.

• Willingness to undergo study procedures, including bone marrow biopsies as detailed in the schedule of events.

• Participants should have received prior treatment with Daratumumab + CyBorD.