Inclusion Criteria:

The main inclusion criteria include but are not limited to the following:

• Has a histologically or cytologically confirmed diagnosis of extensive-stage small cell lung cancer (ES-SCLC)

• For participants receiving gocatamig + ifinatamab deruxtecan (I-DXd) in maintenance only:

  • Completed 3 to 4 cycles of platinum + etoposide chemotherapy with concurrent approved anti-programmed cell death 1/Ligand 1 (anti PD-1/L1) as first line (1L) treatment of ES-SCLC within 6 weeks prior to enrollment
  • No radiological disease progression per Response Evaluation Criteria In Solid Tumors version 1.1 (RECIST 1.1)
  • No other prior systemic ES-SCLC therapy allowed
  • Rechallenge therapy counts as an additional line and leads to exclusion

• For participants receiving gocatamig + I-DXd in induction and maintenance, or gocatamig + I-DXd in induction followed by gocatamig + atezolizumab in maintenance, or carboplatin + etoposide + atezolizumab in induction followed by atezolizumab in maintenance: No prior systemic ES-SCLC treatment allowed

• Applicable to all participants: prior limited-stage small cell lung cancer (SCLC) is allowed if > 6 months have passed since the end of previous therapy and progression

• Must be able to provide a pretreatment archival tumor tissue sample or newly obtained core, incisional, or excisional biopsy of a tumor lesion not previously irradiated

• Measurable disease by RECIST 1.1 as assessed by the local site investigator/radiology. Lesions situated in a previously irradiated area are considered measurable if growth has been shown in such lesions since the completion of radiation

Exclusion Criteria:

The main exclusion criteria include but are not limited to the following:

• Has pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures
• Has any history of interstitial lung disease (ILD)/pneumonitis irrespective of steroid use, current ILD, ILD that cannot be ruled out by imaging at screening, or suspected ILD
• Has clinically severe pulmonary compromise resulting from intercurrent pulmonary illnesses
• Has history of clinically significant intracranial bleeding or spinal cord bleeding
• Has active neurologic paraneoplastic syndrome
• Has history of coronary/peripheral artery bypass graft and/or any coronary/peripheral angioplasty or clinically significant cardiovascular disease such as myocardial infarction, symptomatic congestive heart failure (CHF), and/or uncontrolled cardiac arrhythmia within 6 months before the first dose of study intervention
• Has other uncontrolled or significant protocol specified cardiovascular disease
• Has history of arterial thrombosis within 6 months before the first dose of study intervention
• Has chronic liver disease
• Has history of allogeneic tissue/solid organ transplant
• Has history of leptomeningeal disease
• Is infected with human immunodeficiency virus (HIV) and has a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease
• Has received prior therapy with an anti-programmed cell death protein 1 (anti-PD-1), anti-programmed cell death ligand 1 (anti-PD-L1), or anti-programmed cell death ligand 2 (anti-PD-L2) agent or with an agent directed to another stimulatory or coinhibitory T-cell receptor
• Has received prior radiotherapy within 2 weeks of start of study intervention, or has radiation-related toxicities, requiring corticosteroids
• Has known additional malignancy that is progressing or has required active treatment within the past 3 years
• Has active autoimmune disease that has required systemic treatment in the past 2 years except replacement therapy
• Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis
• Has major surgery within 4 weeks or minor surgery within 2 weeks of allocation/randomization (or first dose), or is anticipated to require a major surgical procedure during the study