The whole gang is on “Abbott Elementary” this season – and we’re referring to the Paddy’s Pub gang. Ahead of the fourth season premiere on Wednesday night (9:30 p.m. ET on ABC), executive producers Justin Halpern and Patrick Schumacker spoke diversity about some of this season’s themes and storylines – including the just-confirmed crossover with It’s Aways Sunny in Philadelphia.

“Sunny” star Rob McElhenney made it official via his social media account last week, posting photos of him and “Abbott” star Quinta Brunson, along with Tyler James Williams and William Stanford Davis of “Abbott” fame and Charlie Day and Danny from “Sunny.” DeVito in front of the Warner Bros. studio lot for “Abbott.” Now, Halpern and Schumacker confirm that the entire It’s Always Sunny in Philadelphia cast will appear in episode 409 and the storyline will take up the full half hour.

“We have the whole gang, the ‘A’ story, ‘B’ story, ‘C’, ‘D’, that’s all of them,” Schumacker said. That means Glenn Howerton (who is currently filming Netflix’s Sirens) and Kaitlin Olsen, who stars in ABC’s High Potential, will also appear. Due to time constraints, a few scenes still need to be filmed for next week’s episode.

“Charlie Day’s character has a pretty important storyline in our episode,” he added. “At first it was a joke that the two shows should overlap. On paper it seems like they’re a real sonic mishmash. But then Rob and Charlie came into our writers’ room and we brainstormed some really rough ideas. From there we emailed beat sheets and then an outline. They were great at everything. Any concerns we had about the tones of the shows clashing were dispelled the moment we started filming with Charlie.”

However, Schumacker said any “Abbott” fans who don’t know “Sunny” shouldn’t feel left out. “It just works in a vacuum,” he said. “They just feel like other guest stars on the show. Obviously it will have a much deeper meaning for ‘Sunny’ fans.”

Will we see the Abbott characters at Paddy’s Pub? “We can’t say much about that yet,” Halpern teased.

There’s also an internal crossover of sorts: “Abbott” executive producer Randall Einhorn also directed several “Sunny” episodes, while “Abbott” screenwriter Jeff Gonzalez also worked on “Sunny” for several seasons has.

Meanwhile, once the “Sunny” stars wrap up their “Abbott” run, they’ll hit the road to film the 17th season of their long-running FX comedy. So is there a chance there could be an Abbott crossover on Sunny? “Great question!” said Schumacker. “I don’t know if we can answer that question now.”

Halpern and Schumacker credited Brunson with first coming up with the crossover idea after running into McElhenney at an event. The duo kept talking (and posting!) about it until it finally became a reality. “In most comedy writers’ rooms, you start the day shitting on other shows that are on TV,” Halpern said. “But that’s not Quinta at all. Quinta comes in and talks about television, which she loves. She has seen every sitcom and loves watching sitcoms. “Sunny” is like a defining show for comedy writers, and so it was like a chance, “one of the shows that we all love, we get a chance to play in their sandbox for a little while.” And it grew from there “That Quinta loves sitcoms and says, ‘I want to do things with other sitcoms that I think are as funny.'”

Meanwhile, there’s a lot more happening at “Abbott Elementary” this season, including a big surprise: a new PGA golf course is being built next to the school, causing many construction issues and concerns about gentrification.

“Each season we try to tackle a bigger issue, with charter schools in Season 2, Janine dealing with the district and seeing it on the other side in Season 3, and then this, with gentrification,” Schumacker said. “The specter of this PGA golf course opening in West Philly will haunt everyone for the duration of the season. A conversation emerges about how these two sides coexist. Do you ultimately have to give and break, or can they possibly coexist?”

And there’s no easy answer, as PGA attorney Miles Nathaniel (played by Matt Oberg) tries to bribe the school with free computers and other perks. “It’s a kind of Faustian bargain,” Schumacker noted. These gifts actually have meaning, which only makes everything more unclear.

“What we’re really trying to do with ‘Abbott’ is to highlight the gray area that exists in all of these issues,” Halpern said. “Like last year in the district, this isn’t just a bunch of big, bad bureaucrats. There are people in it who are trying to do the right thing, and here’s what’s stopping it, and there’s the gray area. It’s the same with charter schools because everyone is the hero of their own story. And yet we’re more interested in what happens to our characters and how it changes the way they think about something or how it causes them to think differently.”

(Incidentally, Halpern revealed that “Miles Nathaniel” is an inside joke that Brunson incorporated into the script. Halpern said his son was originally named “Nathaniel” – but after a few months, he and his wife realized that didn’t fit their child. So they legally changed it to “Miles.”)

This season we will also meet other family members from the core cast that we have not seen yet. And the show will look deeper into the lives of some other characters.

“You’ll see some major storylines of characters where maybe things have changed in their lives, so they’re suddenly open to new journeys in their lives,” Halpern said. “This will allow us to explore all of our characters in a way we haven’t yet. Our goal every season is: What can we do to give each character a new dimension and not just keep making the same jokes? What new can we learn about them? How can we grow them? Even when we talk about her in the writers’ room, there are still big parts of her life that you don’t know as a viewer.”

And no spoilers, but Schumacker added, “There will be a romance from a character you might not expect.” So that’s something to look forward to. And in Season 3, we thought it might be too intrusive with some of the union issues (due to the Hollywood strikes). But we’re exploring that a little bit this season. We have a story arc that deals with a labor movement that directly impacts our characters, and not in the way we expected.”

Then there is the world of “Abbott Elementary.” The set gets bigger and bigger – we see stairs for the first time. And in a Schumacker-directed episode, we’ll see more of what’s actually across the street from the school.

“We now have the teachers’ entrance from the outside,” he said. “We don’t actually have to go to a location anymore, it’s on our back lot. I got to direct Episode 6, and in this episode we actually see the entire physical intersection in front of the student entrance for the first time ever. The deli across the street and the corner store and all that. You can actually see the entire geography and how big our footprint is on the property!”

“Abbott Elementary” fans can also withdraw any remaining “Will They or Won’t They?” Issue. Months after the show’s third season finale finally brought Janine (Brunson) and Gregory (Tyler James Williams) together, there’s still no turning back.

“For us and for Quinta, we’ve always tried very hard not to make this a ‘will-they-won’t-they-Janine and Gregory,'” Halperin said. “Because we have such an incredible ensemble and that’s not what ‘Abbott Elementary’ is about. We asked a lot of things from these characters in the first three seasons, they still had a lot of development to get to this point. And I think there’s a lot to explore as a couple now. This relationship is there and we want to have some fun with it. What can we learn about these two characters that we couldn’t learn in the first three years? But we don’t want it to be the focus of the show.”