A Study of Tarlatamab in Combination With AB248 in Participants With Extensive Stage Small Cell Lung Cancer (DeLLphi-311)

1. Participant has provided informed consent before initiation of any study-specific activities/procedures. 2. Participants ≥ 18 years (or ≥ legal age within the country if it is older than 18 years) at the time of signing the informed consent. 3. Participants with histologically or cytologically confirmed ES-SCLC that has progressed or recurred following at least 1 line of anti-cancer therapy for ES-SCLC. 4. Participants must have at least 1 measurable lesion as defined by RECIST 1.1 within 21-day screening period, not previously irradiated. 5. Participants must have adequate organ function (hematological, coagulation, cardiac, pulmonary, kidney, and liver). 6. Participants must submit a fresh tumor biopsy at screening unless a new biopsy cannot be performed safely or is infeasible. Participants who cannot provide fresh tissue may provide archival tissue that was collected after last anticancer therapy.

1. Symptomatic central nervous system (CNS) metastases. 2. Participants with brain metastases may be eligible if criteria defined in the protocol are met. 3. Prior therapy with any delta-like ligand 3 (DLL3)-directed therapy (including tarlatamab). 4. Prior interleukin (IL)-2, IL-7 or IL-15 targeted therapy. 5. Baseline (at rest) requirement of supplemental oxygen.