I flew CCU-DEL-ORD on one AI ticket on Wednesday last week. Check in staff at CCU asked to all see documents including vaccine card and PCR test. Better to get it done before your first flight. Many check in agents in India still insist on PCR test for US travel. There are random stories of antigen tests getting denied. I would play it safe and get a PCR. Rapid PCR takes 45 minutes and costs like INR 4,000.