Additional Study Information: The purpose of this study is to determine the amount (dose) of telaglenastat that is safe and tolerable when given together with the recommended treatment regimen of pembrolizumab, carboplatin, and pemetrexed and to determine if the combination of standard drugs with telaglenastat is more active against non-small cell lung cancer (NSCLC) than the standard drugs alone. A placebo, which is a tablet containing no telaglenastat medication, but looks identical to telaglenastat will also be used in this study. Telaglenastat is an investigational drug designed to stop cancer from growing by blocking the activity of a protein called glutaminase. The combination of pembrolizumab, carboplatin, and pemetrexed drugs is a recommended treatment for your type of cancer in medical guidelines. Pemetrexed and carboplatin are approved chemotherapy drugs that treat cancer by damaging the cancer cells. These drugs are given together because in combination they are more effective than each drug is individually. This study is a randomized study, meaning you will have a 50% chance of being placed on the study arm that receives plus standard-of-care drugs or you will be placed on the arm that receives telaglenastat.