It's not only ifc, my baby is 3 months, I care for him at home, also going through this phase. Suddenly he can sleep for more than 6 hours straight. If before 12am, I would wake him up at the 4 hour mark, and feed him while he's drowsy, then change his diaper while he's drowsy and he can sometimes sleep all the way to 6/7am. i wake up with my poor engorged boobs throbbing while waiting for him to wake up to feed. 🤣🤣🤣 but I think at this age they are starting to have signs of sleeping through the night.
If you are worried he doesn't get enough, then feed him more (more times or more volume of milk) during the day time. if he needs to eat more, he will let you know. if he is still wetting diapers and pooping consistently then there's no need to worry about him being dehydrated or malnutrition - if he is dehydrated he won't pee, his poop would be pastey and if he is malnutrition he won't gain weight. If hes still active, pee poop as usual, gaining good weight, everything should be fine.