'Family Guy' Cast Reminisces Over Iconic Series as It Hits 400 Episodes: 'Greatest Gig on the Planet'

The cast of Family Guy has plenty to celebrate.

The long-running animated series will air its milestone 400th episode on Fox Sunday night. Titled "Get Stewie," the episode sees Stewie Griffin "in public disgrace after a popstar unleashes her fan base on him for a benign comment," a description of the episode reads.

Elsewhere, Griffin family patriarch Peter Griffin "gets lap band surgery and enjoys the merriment of excess skin."

Ahead of the big premiere, the star-studded voice cast spoke to PEOPLE exclusively about what it means to them for the series to reach 400 episodes.

For Mila Kunis, she's just "so happy for this job."

"This is the greatest gig on the planet," said Kunis, who voices Meg Griffin, at the Family Guy 400th Celebration at the Fox Studios Lot in Los Angeles. "I think I said this — you can find this quote — for 20 years, 'I'm so grateful for this job.' I love everybody here."

After 400 episodes airing across 21 seasons, it's hard for Seth MacFarlane — series creator and voice actor for several of the show's primary characters — to pick a favorite joke that's been told over the years.

"I'd have to sit here for about an hour and think. I'd have to get online and just relive it all," said MacFarlane, 49. "This is really sad. I can't think of one. There's so many. That's like saying what's your favorite song of all time, of any genre? Who can answer that?"

Seth Green, who voices Chris Griffin, thinks it's "crazy" that they've come this far. The series, which premiered in 1999, was originally canceled by Fox in 2002 after three seasons. But when it gained cult popularity, the network decided to revived the series.

In the meantime, Green is looking forward to celebrating the 400th episode milestone.

"I got a pretty good knack for absorbing moments as they happen and not over-processing them, I guess. It's pretty crazy," said the actor, 48. "I'm definitely taking in the fact that this is the longest job I've ever had. How rare it is to have anything last this long with 21 seasons? That's very unlikely."

Green added, "Also, the history of our show. Having been here the whole time, it's also pretty unlikely. So I'm grateful for all of that. I like doing it, so I'm just enjoying it as much as I can."

As for his favorite moment over the years, Green said it's "always the coolest" when they get to do live shows in front of fans.

"There's been a few ticketed shows where we're actually doing a stage reading of it with video and everything. That's really cool," he recalled. "Sometimes just at Comic-Con San Diego, because the fans are all there and those are the best moments because you're just in the booth by yourself. You don't really have any way to gauge if people are laughing at it or anything like that."

As for Alex Borstein, who voices Lois Griffin, she quipped that reaching 400 episodes "means job security."

"It really does. It's been an amazing, amazing, amazing run, and it's like family," said The Marvelous Mrs. Maisel actress, 51. "I haven't seen lot of these people for a couple years now [because of the COVID-19 pandemic]. We were so separated, and this is going to be a really fun reunion once I get in there. It's an unusual situation in Hollywood to have a family that stays together."

Given that the show has now gone on for more than two decades, its longevity going forward is a question for many longtime fans. Borstein, however, would "of course" continue working on the show as long as she can.

"If the show stays on, I'm there. These scripts, every time I read them, I still laugh," she shared. "For me, that's the defining factor. If there's three out loud laughs per script, that's golden, because especially when you work in comedy, you usually don't laugh out loud. So for me, I'm in."

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Family Guy airs Sundays at 9:30 p.m. ET on Fox.