4 week old sleeps all night

My 4 week old baby will sleep the whole night if I let him. Im a light sleeper, so after about 5 hours of sleep he starts to stir and I wake. Usually I will get up to feed him. But tonight I let him be. He will give off the occasional lone cry, and grunt, but when I look over his eyes are still closed and he will stop and look peaceful. Is he trying to wake up? Or just having a light sleeping phase? He slept for 8 hours, until I woke up again and then decided to wake him to eat.

Hes been "sleeping through the night" (5-6 hour stretches) since 2 weeks. He is exclusively breastfed, has gained over 3 pounds and 3 inches qs of his 1 month checkup (he is a growing beanstalk.) So everything is going really well, but Im just concerned about letting him sleep ALL night. It seems to be unusual for his age whenever I research it... thoughts? Looking for reassurance poasibly, or please let me know if this is crazy and I need to set alarms to feed him.