12 week growth spurt or Christmas miracle?!

My LO is 11.5 weeks and has gone from sleeping 3-3.5 hour stretches to 6-7.5 hour stretches at night! It came out of no where and has happened the past 3 nights!! He has reflux so much to my surprise I wasn't expecting him to "sleep through the night" for a very long time! Pray with me that's it's not just a growth spurt and it will stick! How old was yours when they started sleeping 6-7.5 hours at night?