My little man is 4 months and just over a week old... When does the 4 month sleep regression start?

Since birth he's always woken up 2-3 times a night, but the last week he's been sleeping through the night and only waking up once at like 3am. This is extremely different. He slept a full 10 hours the day he turned 4 months? So i'm not sure if he's going backwards or what? Doesn't the sleep regression start around now? He's been extremely good, he only had about 1 day of bad screaming and he's been fine since... it's like it's not even happening, BUT he was 3 weeks early so would that have something to do with it? It'll probably start when he's 5 months? I just don't get what's happening... i keep seeing stories on here that everyone's babies are waking up every hour and not napping, my baby is doing the opposite? Is anyone else's baby sleeping better than ever?