Chord Overstreet is also in talks to return as a series regular, but the number of episodes each castmember will have remains unclear, as does the fate of "Glee Project" Season 1 winners Damian McGinty and Samuel Larsen.

It's official: The entire Glee cast is poised to return for Season 4, but the number of episodes they'll each appear in remains to be seen.

Co-creator Ryan Murphy left the door open for the swelling cast to return, with all 15 regulars -- including Lea Michele, Cory Monteith and Chris Colfer -- accepting the gig, The Hollywood Reporter has confirmed.

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In addition, recurring player Chord Overstreet (Sam) is in talks to rejoin the show as a series regular. Whether The Glee Project Season 1 winners Damian McGinty (Rory) and Samuel Larsen (Joe) return, however, is not yet clear.

The Glee writers returned to work this week and are breaking stories for the upcoming fourth season that will feature a show-within-a-show concept, splitting time between McKinley High in Ohio and following Michele's Rachel Berry in New York as she pursues her Broadway dreams.

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While the status of many of the show's graduating seniors -- Amber Riley (Mercedes), Mark Salling (Puck), Harry Shum Jr. (Mike), Naya Rivera (Santana) and Dianna Agron (Quinn) -- was left up in the air following the Season 3 finale, all are confirmed to return to the Fox juggernaut. However, how many episodes each will film still remains unclear.

Michele, Monteith and Colfer are poised to return as series regulars, among other castmembers THR confirmed, but the number of episodes in which each will appear remains to be seen as writers are working out those details. THR sources remained mum on just who beyond Michele, Monteith and Colfer is classified as a series regular and who will be recurring. Sources told THR that the cast's "series regular" or "recurring" status with the show wouldn't be directly linked to how many episodes each actor appears in as their roles tend to be on an as-needed basis as some recurring players appeared as series regulars in the past.

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"We're literally just writing the first script now," Murphy told THR earlier this month. "We're figuring out who's doing what, who's coming back. We haven't figured it out, but I know what the stories are; I just don't know how many episodes. We want to keep all our options open. I think I have to talk to the actors and say, 'What do you want to do?' That's how we've been dealing with it. I've only talked to Lea so far. That's all happening in the next two weeks."

The unique arrangement allows castmembers to return to Glee as well as continue to explore other projects. Michele, Colfer, Agron and others have landed big-screen roles, while Darren Criss departed the Fox series briefly for Broadway's How to Succeed in Business Without Really Trying. Riley, meanwhile, is focusing on her music career.

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The news comes after a year that saw Michele, Monteith and Colfer's future with the series up in the air as Murphy mulled a New York-set Glee spinoff and after an off-season last year that saw Overstreet part ways with Glee after his series-regular option was not picked up for Season 3. (He later returned as a recurring.)

Also poised to return are Matthew Morrison (Will), Jane Lynch (Sue), Jayma Mays (Emma), Kevin McHale (Artie), Jenna Ushkowitz (Tina), Criss (Blaine) and Heather Morris (Brittany), who will join Season 4 recurring guests including Kate Hudson and Sarah Jessica Parker.

Glee's fourth season premieres in September.

Email: Lesley.Goldberg@thr.com; Twitter: @Snoodit