According to Bob Odenkirk:
'It’s the best season we’ve ever done, it’s going to blow your mind, and I’m not kidding about either of those things. It’s f*cking awesome. I can’t wait for people to see it. It’s just shattering in every direction, and I love it.'
Apparently they are looking at 6 series in total. However, we will have to wait until 2020 for series 5.