Advice CI 3.x or 4.x

Hi,

I'm about to start on a rather large project in php since i've been happily using CI for a few years now i'm going to build the project in CI.
I've noticed that CI 4 alpha 4 has just released. Since my project is due early - mid 2019 i was wondering if you would recommend starting CI4 or build the project in CI 3.1.x?

You've probably gotten this question before, but i'm looking for some advice. 

Sorry for forum spam.

Thanks in advance.

Best regards,
Bart Mommens