Book 7 is due out in August and Book 8 is due out in late 2017 - 10 books total.
Book 6, not 7. Nemesis Games was book 5 only, and Babylon's Ashes (the one this year) is only book 6. Unless you count The Vital Abysss novella as book 6, maybe?
Holy shit that many books? Well I've been looking for some more good sci fi to read so I think I'm going to dive in and start reading them.
They have a contract for 3 trilogies, 9 books total (not 10, but I guess if you count 6 already, that makes 10). They're getting one book a year so far (unlike some author that must not be named).
There's also a few short stories/novellas in ebook form: The Butcher of Anderson Station, Gods of Risk, The Churn, The Vital Abyss. Inequal, but good.
(if you're wondering, The Butcher of Anderson Station is what went into ep 5, "Back to the Butcher", Gods of Risk is about the background & family of one - hopefully - upcoming character for season 2, The Churn is Amos' backstory, which he refers to briefly during ep 7 when he says "welcome to the churn" to Holden, and The Vital Abyss is about Toth Station, which was referred to at the end of ep 10)
Now, I wish the show would be 9 seasons as well. I mean, if you could do 10 seasons of Stargate SG1, you surely can do 9+ of TheExpanse...