As of this writing, Percy Jackson and the Olympians is only green lit for one season. That said, there are larger plans at place for Rick Riordan's world of half-bloods and Greek gods. The author himself has confirmed that the "idea" is to adapt one of his novels per season of the live-action show, starting with The Lightning Thief for Season 1.
"Of course, first we have to get approval to do future seasons," Riordan wrote. "Right now, we are only green-lit for one season, but if you all watch and like it, I am optimistic we will get approval to do more."
That approval is pending, but it sounds like Season 1 is being written a total of five installments in mind. Speaking to IMDb, leading man Walker Scobell joked that he's always asking Riordan questions about the books, including how to pronounce some notable names.
"I've asked like, a million questions about the series," Scobell said. "I think my biggest question is how to pronounce Thalia and Castellan, because it's a huge debate on set. Everyone pronounces it differently."
Thalia is the first name of Thalia Grace, the daughter of Zeus. Fans of the books know Thalia does not debut until the final moments of the second book, The Sea of Monsters, and does not have a pronounced role until the final three books. Regardless, her name is mentioned numerous times in The Lightning Thief, such as her relation to Camp Half-Blood's protective tree and her involvement in the big three's oath about not having children.
Castellan is the last name of Luke Castellan, the son of Hermes. Luke is confirmed to be in Season 1, played by actor Charlie Bushnell, but his amount of screen time is unknown. Luke's most prominent chapters come in later books, once he fully embraces the dark side.
While Luke's last name being spoken on set may not seem like much, the character's lineage plays a major role in the books. His godly parent is known, but the human side of his family tree is kept so secretive that readers do not learn of Luke's last name until the fourth book, The Battle of the Labyrinth.
"Show me your sword, Luke Castellan, the voice of Kronos said. A jolt went through me. I realized I had never heard Luke's last name before. It had never occurred to me." -Percy Jackson & the Olympians: The Battle of the Labyrinth Chapter 50comments
This could mean that the first time viewers hear Luke's last name is expedited to Season 1, or conversations could be happening behind the scenes about how it will be incorporated down the line. Nevertheless, little namedrops like "Thalia" and "Castellan" indicate that there's a much bigger world at play here than just what goes on in Percy's freshman quest.
Percy Jackson and the Olympians is currently in production.