The expanse is based on a 9 books series. Basically seasons 1- 6 are books 1-6. Books 7-9 take place after a substantial time jump in the story and it makes sense to end the tv show there. The writers were involved in the series. I ended up reading the whole series after watching the show. The show makes parts of the books better and the books make parts of the show better. They really compliment each other well. The overall story line is exactly the same.