HBO has locked up its Game of Thrones stars for a potential seventh season of the hit drama.

The principal Thrones actors, who were signed only through six seasons of the show, have completed an extensive renegotiation of their contracts that includes an option for season seven, The Hollywood Reporter has learned.

In exchange for the option, HBO has ponied up huge raises for seasons five, six and the potential season seven that will make the castmembers among the highest-paid actors on cable TV. An HBO rep declined to comment on the renegotiation or the season seven options.

Game of Thrones, based on the best-selling books by George R.R. Martin, was renewed in April for two additional seasons, taking it through season six. A seventh season has not been greenlighted but is considered highly likely given Thrones' status as a ratings smash and awards favorite.

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With one of the largest and most diverse ensemble casts on TV, Thrones employs a tiered system to compensate its stars, according to sources. The "A" tier — which includes actors Kit Harington (Jon Snow), Peter Dinklage (Tyrion Lannister), Lena Headey (Cersei Lannister), Emilia Clarke (Daenerys Targaryen) and Nikolaj Coster-Waldau (Jaime Lannister) — is paid at the highest level. The "A" tier actors are said to have renegotiated their deals in concert.

The lower-salaried "B" tier — which is said to include co-stars Natalie Dormer (Margaery Tyrell), Sophie Turner (Sansa Stark), Maisie Williams (Arya Stark) and others — is said to be scoring raises as well in exchange for season seven options. A still-lower tier of regular actors will receive much smaller pay increases, according to sources.

Renegotiations are common on hit shows, and Thrones is the biggest show on HBO, with its fourth-season finale drawing 7.1 million total viewers. Last season, Thrones topped The Sopranos as HBO's most watched series of all-time in terms of average gross viewership. The series draws a massive 18.6 million viewers across multiple platforms and views. Its viewership overseas is similarly strong.

In addition, the series most recently led the Emmy nominations with 19 total mentions, including best drama series and best drama writing, and supporting drama actor and actress for Dinklage and Headey, respectively. Thrones also has helped its cast land high-profile film projects.

Of course, when an actor signs on for seven seasons of Game of Thrones it doesn't mean his or her character will live that long. Thrones is notorious for killing off characters, and Martin is still finishing the book series on which the show is based, which means the stars could lose their jobs — and their new paychecks — before a seventh season.

Of the "A" tier stars, Harington is repped in the U.S. by CAA, Parseghian Planco and attorney Karl Austen; Dinklage is repped by CAA, Insight and Austen; Headey is repped by CAA, TMT and attorney Roger Haber; Clarke is repped by CAA and Michael Emptage at Emptage-Hallett in the U.K.; and Coster-Waldau is repped by WME, Impression and Lindberg Management.

Tatiana Siegel contributed to this report.

Oct. 29, 11:00 a.m. Updated with HBO's response.

Email: Matthew.Belloni@THR.com

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