My DS slept for about 7 hours straight from 4 weeks old and then the first time he slept through was at 9 weeks old - this was 11 hours straight sleep.

He then didn't sleep through again until 13 weeks. And even now at nearly 4 months old he still doesn't sleep through regularly! Just every now and then. It changes from week to week! ATM he's back to waking after 7 hours sleep again.

So definitely enjoy it while you can.