This study is testing two treatments for a type of lung cancer called **Extensive-Stage Small Cell Lung Cancer (ES-SCLC).** It compares a new drug combination called **BMS-986489** with a drug called **Atezolizumab**. Both treatments are mixed with two other drugs, **Carboplatin** and **Etoposide,** which are usually used to treat this cancer. The study is for people who have not had treatment for this kind of cancer before.

• **Key Point 1:** The study involves several visits and tests, including imaging scans like CT or MRI.
• **Key Point 2:** Participants must be healthy enough to do daily activities with little or no help.
• **Key Point 3:** The study may not be suitable for people with certain health conditions or who have had previous treatments for this cancer.

Participants will need to have at least one tumor outside the brain that can be seen using special scans. If you have certain health problems, like cancer spread to the brain, lung or heart diseases, or nerve damage, you might not be able to join. The study will help doctors understand which treatment works best and is safest for people with ES-SCLC.