The third season of "Game of Thrones" is "probably as big as we're going to get," according to co-showrunner David Benioff, who joined partner D.B. Weiss on a press conference call to preview the HBO fantasy epic's return on Sunday night at 9.

"Season 3 is probably the biggest in terms of the number of new characters, number of new stories overall," Benioff explained. "The universe has expanded as much as it's going to, and now it's going to contract... As pieces start to get removed from the chessboard, we'll have fewer on there. We're nearly to the midpoint (of the story), and it'll be interesting to see what's going forward with the endgame."

The new season brings in a bunch of new characters, including King Beyond the Wall Mance Rayder (Ciaran Hinds), the wise and grandmatronly Olenna (Diana Rigg) and mysterious siblings Jojen and Meera Reed (Thomas Brodie-Sangster and Ellie Kendrick), among others. The season will be adapting, more or less, the first half of George R.R. Martin's third book in the series, "A Storm of Swords," though there are elements from both earlier and later books being included, depending on what makes sense for the TV show.

The Reeds, for instance, first appear in the second book, but Benioff explained that they held them for this season because "We just felt they'd make more impact coming in later... If things get too byzantine, it's so confusing that none of it adds up, and you're spending three minutes with characters per episode, and the whole thing becomes a wash."

Late last season, Benioff, Weiss and their team put together "Blackwater," an episode that stood out from what they'd done before because it featured a battle sequence far bigger in scope than previously, and because it focused entirely on the characters in and around that battle. Weiss called "Blackwater" a "good proof of concept," in that it showed them just how big the could scale things, but Benioff said it would be difficult to use that more intimate storytelling approach regularly because they have too many stories to follow in only 10 episodes. That said, the ninth episode of season 3 will focus on a smaller group of characters, while they expect in season 4(*) to do a battle even bigger than in "Blackwater."

(*) No, "Game of Thrones" has not been officially renewed for a 4th season yet, but that seems a formality more than anything else. Throughout the call, Benioff and Weiss discussed season 4 plans in the sense of when they got to do them, rather than if.

I'll be publishing my review of the new season (I've seen the first four episodes) tomorrow morning, but in the meantime, some other highlights from Benioff and Weiss:

They're as worried about when the remaining books come out as you are: Actually, "I guess we spend more time worrying than the fans," Benioff said. The two of them visited Martin at his home in Santa Fe back in February to pump him for information about where all the stories are going, so they can properly set them up in the world of the show, and "It was incredibly useful," according to Benioff.

"There's no question that this will be better for us if the books come out before the various seasons come out," Benioff added. "That said, we're not going to take a two-year hiatus (to wait for a book). The little kids are growing older, the show's got momentum now, and the show must go on. We're just hopeful that it will all time out."

There's no hard and fast rule for deviating from the books: As with the timing of the Reeds' introduction, Benioff and Weiss look at what will be best for the show, while remaining as faithful as they can to Martin's text. They will also reassign stories that in the books involve minor characters to major ones, as they do early in the new season with something involving Littlefinger (Aidan Gillen) that in the books highlighted someone who's only appeared briefly so far on the show.

"Often times, when in doubt, we'd prefer to have our known characters and our brilliant actors who are with us all the time taking over for our minor characters," said Benioff.

As the show goes on, they may deviate even more: A reporter, without naming names, asked if a character he liked a lot might live on the show rather than dying in the books. Benioff joked, "What's it worth to you?," then noted that while they have yet to spare a character killed by Martin, they've killed a few people on their own.

"I would not rule out the idea that a character who gets whacked in the book series makes it through the TV series," Benioff said.

"Every time we hang with Jason Momoa," Weiss added, "we kick ourselves for not keeping Drogo around, because it's harder to get a party started without him."

Episodes are assembled based largely on how well the pieces fit together: Arya Stark (Maisie Williams) initially appeared in a few scenes in the season 3 premiere, but the producers felt the episode was getting too crowded and moved her scenes back to the second episode. This wasn't the first time, nor will it be the last, where scenes shot for one episode wind up in another, with the only thing restricting them being the idea that each story thread happens in order, roughly in synch with the others.

That means that there's no attempt to come up with individual episodic themes the way that, say, "Mad Men" buildts its hours.

"It's something that in a feature (film) that's contained in two hours, or in a show that's more contained in its characters, it's more workable," said Weiss. "But this is a show about an entire world with many storylines, and to try to cram all the storylines in an episode into one thematic box, more often than not you get something that feels forced. So we have to take a bottom up approach rather than a top down approach. We ask what makes sense of any given storyline we're writing. We feel like if you do your job with writing, the scenes take care of themselves."

Jack Gleeson almost wasn't Joffrey: They had originally cast another actor out of London, and only met with Gleeson because he had already been scheduled for a casting trip to Dublin.

Benioff recalled that Gleeson was a very nice, charming kid, and "when it came time for the audition, it was like he flipped a switch and he became the most despicable teenager on the planet... This is not a Hollywood bullshit thing. He's genuinely one of the sweetest guys I've ever met. We're worried that he's going to wander into a bar one day and some guy who can't separate fact from fiction takes a swing at him."

They think the sexposition talk is overblown: A frustrated Weiss responded to a question about the amount of sex and nudity on the show, and the commentary about it, by saying, "We put in the show what we think belongs in the show. There are going to be people who think there's too much of something, or not enough. If you create a show with a committee of a million people, you're not going to make a very good show. We do what's right to us.

"The only thing that bothers me," he added, "is when people say, 'Oh, you've made it so much more sexual than the books,' which is patently untrue. When you're seeing a person's naked body on screen, it's much more in your face than in the page." He went on to describe a scene Martin wrote for book 5, "A Dance with Dragons," involving eight very naked dancers of both genders having sex with each other as part of the performance, which is something they could never show, "And then there are graphic sexual scenes in the books with 14-year-old girls, which would have us all thrown in prison if we showed them that way."

Alan Sepinwall may be reached at sepinwall@hitfix.com