In specific, The Hollywood Reporter revealed in July that The Dance of the Dragons, the Targaryen civil conflict that House of the Dragon will depict, is currently expected to only span about three or four seasons.
The outlet does note in the same piece that Sapochnik and Condal are open to keeping House of the Dragon going past The Dance of the Dragons by adopting an anthology-esque approach for the series. Essentially, that would mean that future, post-Dance seasons of House of the Dragon could focus on other iconic Targaryen moments from Westerosi history, including Aegon’s Conquest.
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Why 'House of the Dragon' probably won’t be as long as Game of Thrones