How long does baby sleep?

My 13 month old was sleeping on average 11.5 hours at night with only one nap during the day. The last week, she's been sleeping only 8 hours at night but still 1 nap a day. Im struggling a bit because my 3 month still wakes up at least twice a night. Im wondering if this is a phase and my 13 month old might go back to sleeping almost 12 hours or is 8 hours as good as it gets? Anybody else have a LO that has drastically changed how long they sleep at night?