This is an open-label, ascending, multiple doses, phase 1 study evaluating tarlatamab monotherapy, in combination with anti-PD1 therapy and with additional cytokine release syndrome (CRS) mitigation strategies. Tarlatamab will be administered as a short term intravenous (IV) infusion in participants with SCLC. Tarlatamab is a Half-Life Extended (HLE) Bispecific T cell engager (BiTE®) targeting delta-like protein 3 (DLL3)