How much of The Expanse's book series has yet to be adapted into live-action? Starting life on the Syfy channel, The Expanse has steadily built a cult following over the course of 4 tightly-woven seasons. Based on the series of novels by James S. A. Corey, The Expanse follows the adventures of every-man ice hauler James Holden, who becomes accidentally embroiled in a conspiracy that stretches across the solar system and beyond. Reluctantly assuming responsibility for a ragtag crew, Holden becomes the epicenter of mankind's first contact with an alien sentience, while simultaneously trying to stop a war breaking out between Earth, Mars and the Belt.
Despite retaining a passionate following, The Expanse only lasted 3 seasons on the Syfy channel before cancellation beckoned, but fans didn't take the decision lying down. An online campaign to save The Expanse began, with efforts focused on attracting streaming services into rescuing the property. Before long, Amazon Prime picked up the adrift science fiction series, confirming The Expanse would run for at least 2 more seasons. Season 4 finally released in late 2019 and season 5 is still on the horizon, but how far into the original novels has The Expanse's story come, and how much remains?
The Expanse TV series has progressed at a rate of roughly one book per season, albeit with a little bit of overlap. The most recent season (the one that premiered on Amazon Prime) was largely comprised of material from the fourth book, Cibola Burn, and ends by establishing Marco Inaros and his Free Navy as the series' next major villains. With Marco coming into prominence, The Expanse season 5 is likely to be combination of the fifth and sixth novels, Nemesis Games and Babylon's Ashes. With 2 more books still left untouched after that, The Expanse potentially has enough material to run all the way to season 8, although whether it reaches that point remains to be seen.
It's also important to consider that the original Expanse book series has yet to conclude. A final, as yet untitled, novel is expected to release sometime in 2020 and will round-off the story of The Expanse. Depending on how much material is crammed into this ultimate installment, The Expanse may find itself with enough story to run to a tenth season. Reaching double digits would be a hugely impressive and unlikely feat for a series of The Expanse's nature, and it wouldn't be unusual to see the show start to accelerate if a sixth season is green-lit by Amazon. Having said that, The Expanse's cast and crew spoke very positively about the creative freedom they were afforded at Amazon, and the fourth season certainly takes its time in exploring the story of Cibola Burn. As long as The Expanse remains popular, perhaps Amazon will hold faith all the way to season 9 or 10, especially with streaming requiring a steady supply of original content.
Truthfully, even fans who campaigned for The Expanse's survival after season 3 likely don't seriously expect the series to run for another 5 or 6 years. The adventures of the Rocinante demand no small amount of visual effects and actors have a tendency to seek other career opportunities after a while. As long as The Expanse has time to resolve its main storylines and isn't forced into a rushed conclusion, and as long as it doesn't end on a massive reveal (as almost happened before Amazon stepped in) most viewers will likely be satisfied enough.
The Expanse season 5 is currently without a release date.