"We just finished editing the [season 8] finale," Nicotero said during a Facebook Live session, where he was joined by stars Christian Serratos, Ross Marquand, Austin Amelio, Tom Payne and Steven Ogg.
"Which feels weird, because we shot in November and we're still working on posting the show and doing the visual effects," Nicotero explained. "And you guys are doing [additional dialogue recording] and every once in a while you get called to record some additional stuff, so we're still finishing last season and then we just started season 9."
"So you guys are gonna be busy, all I can say," Nicotero said.
"We just did the pitch out for season 9, and there's some really cool stuff coming," Kirkman told Screen Junkies News, where he promised cool developments from special effects guru Nicotero.
"In the pitch, Greg was like, 'oh, I can't wait to get started on that!' I was like, 'I can't wait to see that,'" Kirkman said. "They're always coming up with cool new evolutions for the zombies and there's some big stuff coming up in season 9 that I'm hinting at and I'll probably get in trouble for, zombie-wise."
Kirkman said one of the biggest twists of season 8 — where Carl Grimes, who serves as deuteragonist in his ongoing comic book series, was brazenly killed off — will make for a more unpredictable show come season 9.
"Really if anything, [Carl's death] just makes me more excited," Kirkman told Talking Dead. "I think that any time that path is not set, any time you can't look at a comic book series and go, 'oh, I know exactly what's going to happen,' it makes things a little bit more exciting."
"And dealing with those unknowns," Kirkman added, "when we're in the writers room, when we're working on season 9, all those changes that kind of snowball out from that, it just makes for a better show."
Earlier this month, all major Walking Dead cast members save for Lauren Cohan re-signed to return for season 9, expected to debut this October on AMC.
The Walking Dead airs Sundays at 9/8c on AMC.